[1.2.X] Added additional information on what the APPEND_SLASH setting does....

[1.2.X] Added additional information on what the APPEND_SLASH setting does. Thanks to ttencate for the report and draft text.

Backport of [14110] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14111 bcc190cf-cafb-0310-a4f2-bffc1f526a37