Add managed models to changelog

CHANGELOG.rst

@@ -9,12 +9,17 @@ and this project adheres to `Semantic Versioning`_.
 Unreleased
 ----------
 
+The "managed models" feature is mandatory for all models derived from `ExtensibleModel`
+and requires creating a migration for all downstream models to add the respective
+field.
+
 Added
 ~~~~~
 
 * Frontend for managing rooms.
 * [Dev] Components for implementing standard CRUD operations in new frontend.
 * [Dev] Options for filtering and sorting of GraphQL queries at the server.
+* [Dev] Managed models for instances handled by other apps.
 
 Changed
 ~~~~~~~