Better documentation

This pull request includes:
* Better documentation about using Stockfish in command-line mode.
* Better documentation about Stockfish's various UCI options.

Some of the info is taken from the stockfish support website, and some is new.

I think putting it all in one place is good for the user so that he/she does not have to scourge through forums and support articles.

I hope you like this small gift before you pull the trigger on SF 5. :)