Feature/GitHub getting started

This is a terminal yank of the primer to github that dzmitry did. let me know of any changes tha you feel would be appropriate.  I plan to add additional comments to this document soon.
you can add here:
```git diff HEAD```      # show what changed since last commit 
```git diff```                 # show what has changed but has not been added via ```git add```
```git diff --cached```  # show what has been added via ```git add``` but not yet committed