Update realtransforms.py

The docstring for dst has errors for **type II**.  I've updated the docstring according to the information on the wikipedia DST page.  As far as I can tell, the description at wikipedia is accurate, and can be used for the docstring.
DOC: link to numpydoc via a git submodule
Merge pull request #2657 from pv/numpydoc

DOC: link to numpydoc via a git submodule
Merge pull request #2656 from arichar6/patch-1

Update realtransforms.py, to correct docstring for dst.