Merge pull request #20337 from edx/ormsbee/user_authn_readme

Update user_authn README to new format.

openedx/core/djangoapps/user_authn/README.rst

-The ``user_authn`` app contains user authentication related features such as
-login and registration.
+Status: Maintenance
 
-* Ideally this would be in its own service, but at this point, LMS is the home
-  of all authentication related features.
+Responsibilities
+================
+The ``user_authn`` app contains user authentication related features such as login and registration.
 
-* At this time, these features are still plugged into Studio. Future clean-up
-  in Studio is intended to make this an LMS only feature.
+Direction: Extract
+==================
+Ideally this would be in its own service, but at this point, LMS is the home of all authentication related features.
+
+At this time, these features are still plugged into Studio. Future clean-up in Studio is intended to make this an LMS only feature.
+
+Glossary
+========
+
+More Documentation
+==================