https://www.codeschool.com/paths/git
http://nyuccl.org/pages/GitTutorial/
http://rogerdudler.github.io/git-guide/
http://kbroman.org/github_tutorial/
http://www.scfbm.org/content/8/1/7
https://blog.bitbucket.org/2013/03/19/introducing-sourcetree-git-client-microsoft-windows/