fix: do not use appname for config extension entry points

docs/glossary.rst

@@ -137,6 +137,8 @@ Glossary
       The intention is that all config extensions will have been
       applied before the :term:`app handler` is created.
 
+      See also :ref:`config-extensions`.
+
    config file
      A file which contains :term:`config settings<config setting>`.
      See also :doc:`narr/config/files`.

docs/narr/config/object.rst

@@ -56,6 +56,8 @@ to solve the "chicken-vs-egg" problem::
    app = config.get_app()
 
 
+.. _config-extensions:
+
 Extending the Config Object
 ---------------------------