DOC: Added get_group() example to grouby.html
Added a get_group example in the Iterating through groups section of grouby.html to demonstrate selecting
single group from a DataFrameGrouBy object

Fixed typo in README

Looking good. Can you just squash the commits into one?
 can u make this into a sub-section as well 
 rebase again. We had an unrelated failure.
 Thanks a lot!
