Fixed #20690 -- Mentioned LOCALE_PATHS earlier in translation docs.

Thanks rene@ for the suggestion.

docs/topics/i18n/translation.txt

@@ -1242,9 +1242,11 @@ The script should be run from one of two places:
 * The root directory of your Django app.
 
 The script runs over your project source tree or your application source tree
-and pulls out all strings marked for translation. It creates (or updates) a
-message file in the directory ``locale/LANG/LC_MESSAGES``. In the ``de``
-example, the file will be ``locale/de/LC_MESSAGES/django.po``.
+and pulls out all strings marked for translation (see
+:ref:`how-django-discovers-translations` and be sure :setting:`LOCALE_PATHS`
+is configured correctly). It creates (or updates) a message file in the
+directory ``locale/LANG/LC_MESSAGES``. In the ``de`` example, the file will be
+``locale/de/LC_MESSAGES/django.po``.
 
 By default :djadmin:`django-admin.py makemessages <makemessages>` examines every
 file that has the ``.html`` or ``.txt`` file extension. In case you want to