Fixed #14835 -- Corrected a lack of indentation in the reST markup fo…

…r docs/ref/contrib/admin/index.txt and reflowed the text accordingly. Thanks to cogat for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14830 bcc190cf-cafb-0310-a4f2-bffc1f526a37