Fixed #17053 - Added a note about USE_THOUSAND_SEPARATOR setting to localizations docs.

Thanks shelldweller for the draft patch.

docs/topics/i18n/formatting.txt

@@ -21,7 +21,10 @@ necessary to set :setting:`USE_L10N = True <USE_L10N>` in your settings file.
 
     The default :file:`settings.py` file created by :djadmin:`django-admin.py
     startproject <startproject>` includes :setting:`USE_L10N = True <USE_L10N>`
-    for convenience.
+    for convenience.  Note, however, that to enable number formatting with
+    thousand separators it is necessary to set :setting:`USE_THOUSAND_SEPARATOR
+    = True <USE_THOUSAND_SEPARATOR>` in your settings file. Alternatively, you
+    could use :tfilter:`intcomma` to format numbers in your template.
 
 .. note::