Fixed #25447 -- Emphasized the need to restart dev server when adding template tags.

docs/howto/custom-template-tags.txt

@@ -22,8 +22,12 @@ described below are automatically made available to load within templates.
 The app should contain a ``templatetags`` directory, at the same level as
 ``models.py``, ``views.py``, etc. If this doesn't already exist, create it -
 don't forget the ``__init__.py`` file to ensure the directory is treated as a
-Python package. After adding this module, you will need to restart your server
-before you can use the tags or filters in templates.
+Python package.
+
+.. admonition:: Development server won't automatically restart
+
+    After adding the ``templatetags``  module, you will need to restart your
+    server before you can use the tags or filters in templates.
 
 Your custom tags and filters will live in a module inside the ``templatetags``
 directory. The name of the module file is the name you'll use to load the tags