provide docs for Rubinius-specific things about the ruby implementation

this is a reference to this issue : rubinius/rubinius#3709

Here I'll just put the list sorted by importance(for me :) ) :
1-the standard library architecture(to what gems it's seperated, how to find them, etc).
2-the debugger.
3-the profiler.
4-the C-API.
5-hmm maybe some troubleshooting for rubinius-specific problems.

[brixen]

@abnud1 thanks for opening this.