badge the README so things don't get broken, maybe.

README.rst

@@ -4,6 +4,10 @@
 .. image:: https://travis-ci.org/zopefoundation/zope.intid.png?branch=master
         :target: https://travis-ci.org/zopefoundation/zope.intid
 
+.. image:: https://readthedocs.org/projects/zopeintid/badge/?version=latest
+         :target: http://zopeintid.readthedocs.io/en/latest/?badge=latest
+         :alt: Documentation Status
+
 This package provides an API to create integer ids for any object. Later
 objects can be looked up by their id as well. This functionality is commonly
 used in situations where dealing with objects is undesirably, such as in