Git Procedure and Readme.md

I wrote up some of what seems to have been the standard github procedure for the past couple of semesters into a new github Readme.md file.  This is a rough draft/first attempt.  In particular Davide probably has something to say about it.  It also may be too long for a README.md file since it covers everything from setting up github to develop, to code workflow, to creating pull requests, to reviewing pull requests.  

Rather than have everyone go back and force with commits (which seems inefficient for editing a readme), I've posted the content of the README.md file at: 

https://github.com/openwebwork/webwork2/wiki/Github-Protocal-(New-Readme.md-page)

Feel free to edit it/make changes/whatever.  After people are pretty happy with it, I'll copy the contents of the wiki over into the README.md file as a commit.  

P.S.  After we are happy with this I'll create pull requests to release/2.9 and develop and will work up a PG version of the same thing.