Added a link to the "documentation" documentation in the contributing docs.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9192 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/internals/contributing.txt

@@ -608,6 +608,10 @@ General improvements, or other changes to the APIs that should be emphasized
 should use the ".. versionchanged:: X.Y" directive (with the same format as the
 ``versionadded`` mentioned above.
 
+There's a full page of information about the :ref:`Django documentation
+system <internals-documentation>` that you should read prior to working on the
+documentation.
+
 Guidelines for ReST files
 -------------------------