Fixed #20284 - Added a note about DEBUG in static file docs.

4. Store your static files in a folder called ``static`` in your app. For

   example ``my_app/static/my_app/myimage.jpg``.

Now, if you use ``./manage.py runserver``, all static files should be served

automatically at the :setting:`STATIC_URL` and be shown correctly.

.. admonition:: Serving the files

    In addition to these configuration steps, you'll also need to actually

    serve the static files.

    During development, this will be done automatically if you use

    :djadmin:`runserver` and :setting:`DEBUG` is set to ``True`` (see

    :func:`django.contrib.staticfiles.views.serve`).

    This method is **grossly inefficient** and probably **insecure**,

    so it is **unsuitable for production**.

    See :doc:`/howto/static-files/deployment` for proper strategies to serve

    static files in production environments.

Your project will probably also have static assets that aren't tied to a

particular app. In addition to using a ``static/`` directory inside your apps,