RTD link for django-config-models is broken

, as far as I can tell, the link (which I found only at https://github.com/edx/django-config-models/blob/master/README.rst) isn't a broken link that I can fix, but rather refers to documentation that may never have existed on readthedocs.io.

There are docs in django-config-models/docs/ , but I don't know if they're complete enough for us to want to publish them on readthedocs.

So, I think the short term fix is to remove the https://github.com/edx/django-config-models#documentation section. Then, we can decide what documentation we want to have in this area and how we want to deliver it – within the repo, on readthedocs, in Confluence, or whatever.