Add Cheat Sheet FR

All the content fits and looks great, with one exception for the Synchroniser les Changements (Synchronize Changes) section description. I'm hoping there's a way this description can be shortened or translated in a different way to be just a few characters shorter.

@kamon, would you mind opening a Pull Request against [the markdown file](https://github.com/github/training-kit/blob/master/downloads/fr/github-git-cheat-sheet.md) and helping with this? Thanks! 

![screen shot 2014-06-09 at 2 42 46 pm](https://cloud.githubusercontent.com/assets/352082/3222466/ad3641c6-f016-11e3-899d-c0f632652ecc.png)