Fixed #12941 -- Added documentation for the connections dictionary. Thanks to...

Fixed #12941 -- Added documentation for the connections dictionary. Thanks to atlithorn@gmail.com for the report, and Alex Gaynor for the original text.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12709 bcc190cf-cafb-0310-a4f2-bffc1f526a37