README.rst: Update Static URL (point to PyPI)

$ wget -S http://lukearno.com/projects/static/
 ...
 HTTP request sent, awaiting response...
   HTTP/1.1 404 Not Found
   ...
 2013-09-20 07:53:36 ERROR 404: Not Found.

PyPI still points to lukearno.com as the home page, but we can expect the PyPI
URL to age better.