Fixed #15592 -- corrected an missing backtick in the syndication docs. Thanks...

Fixed #15592 -- corrected an missing backtick in the syndication docs. Thanks to bradley.ayers for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15793 bcc190cf-cafb-0310-a4f2-bffc1f526a37