DOC: add pandas sprint whatsnew entry
@datapythonista @jorisvandenbossche @TomAugspurger 

We should add a short section in the whatsnew: http://pandas-docs.github.io/pandas-docs-travis/whatsnew.html#documentation-changes

That gives recognition to the PR's for the sprint. We *could* list the PR's numbers, or maybe just a link to a gtihub search which shows them would be ok too.