README: expand with "Running Geth" section

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@@ -54,6 +54,197 @@ The go-ethereum project comes with several wrappers/executables found in the `cm
 | `gethrpctest` | Developer utility tool to support our [ethereum/rpc-test](https://github.com/ethereum/rpc-tests) test suite which validates baseline conformity to the [Ethereum JSON RPC](https://github.com/ethereum/wiki/wiki/JSON-RPC) specs. Please see the [test suite's readme](https://github.com/ethereum/rpc-tests/blob/master/README.md) for details. |
 | `rlpdump` | Developer utility tool to convert binary RLP ([Recursive Length Prefix](https://github.com/ethereum/wiki/wiki/RLP)) dumps (data encoding used by the Ethereum protocol both network as well as consensus wise) to user friendlier hierarchical representation (e.g. `rlpdump --hex CE0183FFFFFFC4C304050583616263`). |
 
+## Running geth
+
+Going through all the possible command line flags is out of scope here (please consult our
+[CLI Wiki page](https://github.com/ethereum/go-ethereum/wiki/Command-Line-Options)), but we've
+enumerated a few common parameter combos to get you up to speed quickly on how you can run your
+own Geth instance.
+
+### Full node on the main Ethereum network
+
+By far the most common scenario is people wanting to simply interact with the Ethereum network:
+create accounts; transfer funds; deploy and interact with contracts. For this particular use-case
+the user doesn't care about years-old historical data, so we can fast-sync quickly to the current
+state of the network. To do so:
+
+```
+$ geth --fast --cache=512 console
+```
+
+This command will:
+
+ * Start geth in fast sync mode (`--fast`), causing it to download more data in exchange for avoiding
+   processing the entire history of the Ethereum network, which is very CPU intensive.
+ * Bump the memory allowance of the database to 512MB (`--cache=512`), which can help significantly in
+   sync times especially for HDD users. This flag is optional and you can set it as high or as low as
+   you'd like, though we'd recommend the 512MB - 2GB range.
+ * Start up Geth's built-in interactive [JavaScript console](https://github.com/ethereum/go-ethereum/wiki/JavaScript-Console),
+   (via the trailing `console` subcommand) through which you can invoke all official [`web3` methods](https://github.com/ethereum/wiki/wiki/JavaScript-API)
+   as well as Geth's own [management APIs](https://github.com/ethereum/go-ethereum/wiki/Management-APIs).
+   This too is optional and if you leave it out you can always attach to an already running Geth instance
+   with `geth --attach`.
+
+### Full node on the Ethereum test network
+
+Transitioning towards developers, if you'd like to play around with creating Ethereum contracts, you
+almost certainly would like to do that without any real money involved until you get the hang of the
+entire system. In other words, instead of attaching to the main network, you want to join the **test**
+network with your node, which is fully equivalent to the main network, but with play-Ether only.
+
+```
+$ geth --testnet --fast --cache=512 console
+```
+
+The `--fast`, `--cache` flags and `console` subcommand have the exact same meaning as above and they
+are equially useful on the testnet too. Please see above for their explanations if you've skipped to
+here.
+
+Specifying the `--testnet` flag however will reconfigure your Geth instance a bit:
+
+ * Instead of using the default data directory (`~/.ethereum` on Linux for example), Geth will nest
+   itself one level deeper into a `testnet` subfolder (`~/.ethereum/testnet` on Linux).
+ * Instead of connecting the main Ethereum network, the client will connect to the test network,
+   which uses different P2P bootnodes, different network IDs and genesis states.
+
+*Note: Although there are some internal protective measures to prevent transactions from crossing
+over between the main network and test network (different starting nonces), you should make sure to
+always use separate accounts for play-money and real-money. Unless you manually move accounts, Geth
+will by default correctly separate the two networks and will not make any accounts available between
+them.*
+
+### Programatically interfacing Geth nodes
+
+As a developer, sooner rather than later you'll want to start interacting with Geth and the Ethereum
+network via your own programs and not manually through the console. To aid this, Geth has built in
+support for a JSON-RPC based APIs ([standard APIs](https://github.com/ethereum/wiki/wiki/JSON-RPC) and
+[Geth specific APIs](https://github.com/ethereum/go-ethereum/wiki/Management-APIs)). These can be
+exposed via HTTP, WebSockets and IPC (unix sockets on unix based platroms, and named pipes on Windows).
+
+The IPC interface is enabled by default and exposes all the APIs supported by Geth, whereas the HTTP
+and WS interfaces need to manually be enabled and only expose a subset of APIs due to security reasons.
+These can be turned on/off and configured as you'd expect.
+
+HTTP based JSON-RPC API options:
+
+  * `--rpc` Enable the HTTP-RPC server
+  * `--rpcaddr` HTTP-RPC server listening interface (default: "localhost")
+  * `--rpcport` HTTP-RPC server listening port (default: 8545)
+  * `--rpcapi` API's offered over the HTTP-RPC interface (default: "eth,net,web3")
+  * `--rpccorsdomain` Comma separated list of domains from which to accept cross origin requests (browser enforced)
+  * `--ws` Enable the WS-RPC server
+  * `--wsaddr` WS-RPC server listening interface (default: "localhost")
+  * `--wsport` WS-RPC server listening port (default: 8546)
+  * `--wsapi` API's offered over the WS-RPC interface (default: "eth,net,web3")
+  * `--wsorigins` Origins from which to accept websockets requests
+  * `--ipcdisable` Disable the IPC-RPC server
+  * `--ipcapi` API's offered over the IPC-RPC interface (default: "admin,debug,eth,miner,net,personal,shh,txpool,web3")
+  * `--ipcpath` Filename for IPC socket/pipe within the datadir (explicit paths escape it)
+
+You'll need to use your own programming environments' capabilities (libraries, tools, etc) to connect
+via HTTP, WS or IPC to a Geth node configured with the above flags and you'll need to speak [JSON-RPC](http://www.jsonrpc.org/specification)
+on all transports. You can reuse the same connection for multiple requests!
+
+**Note: Please understand the security implications of opening up an HTTP/WS based transport before
+doing so! Hackers on the internet are actively trying to subvert Ethereum nodes with exposed APIs!
+Further, all browser tabs can access locally running webservers, so malicious webpages could try to
+subvert locally available APIs!**
+
+### Operating a private network
+
+Maintaining your own private network is more involved as a lot of configurations taken for granted in
+the official networks need to be manually set up.
+
+#### Defining the private genesis state
+
+First, you'll need to create the genesis state of your networks, which all nodes need to be aware of
+and agree upon. This consists of a small JSON file (e.g. call it `genesis.json`):
+
+```json
+{
+  "alloc"      : {},
+  "coinbase"   : "0x0000000000000000000000000000000000000000",
+  "difficulty" : "0x20000",
+  "extraData"  : "",
+  "gasLimit"   : "0x2fefd8",
+  "nonce"      : "0x0000000000000042",
+  "mixhash"    : "0x0000000000000000000000000000000000000000000000000000000000000000",
+  "parentHash" : "0x0000000000000000000000000000000000000000000000000000000000000000",
+  "timestamp"  : "0x00"
+}
+```
+
+The above fields should be fine for most purposes, although we'd recommend changing the `nonce` to
+some random value so you prevent unknown remote nodes from being able to connect to you. If you'd
+like to pre-fund some accounts for easier testing, you can populate the `alloc` field with account
+configs:
+
+```json
+"alloc": {
+  "0x0000000000000000000000000000000000000001": {"balance": "111111111"},
+  "0x0000000000000000000000000000000000000002": {"balance": "222222222"}
+}
+```
+
+With the genesis state defined in the above JSON file, you'll need to initialize **every** Geth node
+with it prior to starting it up to ensure all blockchain parameters are correctly set:
+
+```
+$ geth init path/to/genesis.json
+```
+
+#### Creating the rendezvous point
+
+With all nodes that you want to run initialized to the desired genesis state, you'll need to start a
+bootstrap node that others can use to find each other in your network and/or over the internet. The
+clean way is to configure and run a dedicated bootnode:
+
+```
+$ bootnode --genkey=boot.key
+$ bootnode --nodekey=boot.key
+```
+
+With the bootnode online, it will display an [`enode` URL](https://github.com/ethereum/wiki/wiki/enode-url-format)
+that other nodes can use to connect to it and exchange peer information. Make sure to replace the
+displayed IP address information (most probably `[::]`) with your externally accessible IP to get the
+actual `enode` URL.
+
+*Note: You could also use a full fledged Geth node as a bootnode, but it's the less recommended way.*
+
+#### Starting up your member nodes
+
+With the bootnode operational and externally reachable (you can try `telnet <ip> <port>` to ensure
+it's indeed reachable), start every subsequent Geth node pointed to the bootnode for peer discovery
+via the `--bootnodes` flag. It will probably also be desirable to keep the data directory of your
+private network separated, so do also specify a custom `--datadir` flag.
+
+```
+$ geth --datadir=path/to/custom/data/folder --bootnodes=<bootnode-enode-url-from-above>
+```
+
+*Note: Since your network will be completely cut off from the main and test networks, you'll also
+need to configure a miner to process transactions and create new blocks for you.*
+
+#### Running a private miner
+
+Mining on the public Ethereum network is a complex task as it's only feasible using GPUs, requiring
+an OpenCL or CUDA enabled `ethminer` instance. For information on such a setup, please consult the
+[EtherMining subreddit](https://www.reddit.com/r/EtherMining/) and the [Genoil miner](https://github.com/Genoil/cpp-ethereum)
+repository.
+
+In a private network setting however, a single CPU miner instance is more than enough for practical
+purposes as it can produce a stable stream of blocks at the correct intervals without needing heavy
+resources (consider running on a single thread, no need for multiple ones either). To start a Geth
+instance for mining, run it with all your usual flags, extended by:
+
+```
+$ geth <usual-flags> --mine --minerthreads=1 --etherbase=0x0000000000000000000000000000000000000000
+```
+
+Which will start mining bocks and transactions on a single CPU thread, crediting all proceedings to
+the account specified by `--etherbase`. You can further tune the mining by changing the default gas
+limit blocks converge to (`--targetgaslimit`) and the price transactions are accepted at (`--gasprice`).
+
 ## Contribution
 
 Thank you for considering to help out with the source code! We welcome contributions from