Explained why admindocs omits model methods with arguments.

docs/ref/contrib/admin/admindocs.txt

@@ -12,9 +12,14 @@ docstrings of models, views, template tags, and template filters for any app in
 :setting:`INSTALLED_APPS` and makes that documentation available from the
 :mod:`Django admin <django.contrib.admin>`.
 
-In addition to providing offline documentation for all template tags and
-template filters that ship with Django, you may utilize admindocs to quickly
-document your own code.
+You may, to some extent, utilize :mod:`~django.contrib.admindocs` to quickly
+document your own code. This has limited usage, however, as the app is
+primarily intended for documenting templates, template tags, and filters.
+For example, model methods that require arguments are purposefully omitted
+from the documentation because they can't be invoked from templates. The app
+can still be useful since it doesn't require you to write any extra
+documentation (besides docstrings) and is conveniently available from the
+:mod:`Django admin <django.contrib.admin>`.
 
 Overview
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