Clarify guidance for preventing swappable migrations.

docs/backend_architecture/upgrade.rst

@@ -21,10 +21,10 @@ strings should have no prefix (``u`` or ``b``) and the migration should contain
 ``from __future__ import unicode_literals`` as an import.
 
 For any migrations involving Foreign keys to the FacilityUser model, the migration
-will automatically be generated to use a swappable dependency on settings.AUTH_USER_MODEL.
-This should be changed to remove the swappable dependency, set a fixed migration dependency
-and remove the AUTH_USER_MODEL setting from the settings file. FacilityUser should be used
-instead.
+will automatically be generated by Django to use a swappable dependency on settings.AUTH_USER_MODEL.
+This should be updated by removing the swappable dependency, setting a fixed migration dependency
+and replacing the reference to `settings.AUTH_USER_MODEL` with `"kolibriauth.FacilityUser"`
+instead. For an example of this, see this previous pull request: https://github.com/learningequality/kolibri/pull/11984 .
 
 We also use the upgrade functionality triggered during the CLI
 initialization to copy in new copies of static files that are used in the frontend