Add Markdown Cheat Sheet

[pheraph]

A Markdown Cheat Sheet (maybe similar to the github thing) would be nice, especially for which Syntax-highlighter languages are supported.

[hmans]

It's a good idea! I definitely want to add this. However, it'll have to wait for the next big release, since a lot of things are going to change there (most of all syntax highlighter). It's coming, though.

Thanks!