DOC: add pandas sprint whatsnew entry #20515
Description
@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.