Git cheat sheet web-layout mimicking print

A first draft with minimally invasive markup in the markdown, and using common site-wide styles to mimic the [print-ready](https://training.github.com/kit/downloads/github-git-cheat-sheet.pdf) layouts of the cheat sheet.

![screen shot 2014-12-30 at 10 41 38 pm](https://cloud.githubusercontent.com/assets/352082/5585771/085ae0d0-9075-11e4-985e-099a858283d8.png)