message: Mention missing Extend implementation for ImportObject
diff: @@ -291,6 +291,9 @@ removed.
  The `call_state_creator` method is new, along with `get_export` and
  `clone_ref`.
  +The `Extend<(String, String, Export)>` implementation and `extend` method
  +have been removed. Namespaces must now be final when `register`ed.
  +
  ### `Instance`
  Before:
  