Fixed #14403 -- Provided some extra resources on the difference between...

Fixed #14403 -- Provided some extra resources on the difference between FloatField and DecimalField in the model field reference. Thanks to typeshige for the report and trebor74hr and dmedvinsky for the draft patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15090 bcc190cf-cafb-0310-a4f2-bffc1f526a37