Fixed #21948 -- Noted TEMPLATE_LOADERS requirement when overriding admin templates.

In order to override one or more of them, first create an ``admin`` directory

in your project's ``templates`` directory. This can be any of the directories

you specified in :setting:`TEMPLATE_DIRS`.

you specified in :setting:`TEMPLATE_DIRS`. If you have customized the

:setting:`TEMPLATE_LOADERS` setting, be sure

``'django.template.loaders.filesystem.Loader'`` appears before

``'django.template.loaders.app_directories.Loader'`` so that your custom

templates will be found by the template loading system before those that are

included with :mod:`django.contrib.admin`.

Within this ``admin`` directory, create sub-directories named after your app.

Within these app subdirectories create sub-directories named after your models.