Added grouby apply notebook
Here is a notebook I created with help at the pandas dev sprint in Montreal.  

Its meant to help document the behavior in issue 9867: It's difficult to predict what DataFrame.groupby().apply() will return

https://github.com/pydata/pandas/issues/9867

@mbirdi could you put this notebook in a [gist](https://gist.github.com/) share a link to the preview on [nbviewer](http://nbviewer.ipython.org/)? I don't think we actually want to merge this into the pandas repo :).
 @shoyer 

Thanks for the tips.  I used gist and and nbviewer.  It looks like it worked from my side.  I think this link should be viewable by others.

http://nbviewer.ipython.org/gist/mbirdi/05f8a83d340476e5f03a
 @mbirdi OK, thanks! I added a link to that notebook from the original issue.
