Update 5.0.md to include installed apps for Query change (#11718)

* Update 5.0.md to include installed apps for Query change
# Conflicts:
#	CONTRIBUTORS.md

docs/releases/5.0.md

@@ -279,6 +279,8 @@ The undocumented `Page.get_static_site_paths` method (which returns a generator
 The `wagtailsearch.Query` model has been moved from the `search` application to the contrib application `wagtail.contrib.search_promotions`.
 All imports will need to be updated and migrations will need to be run via a management command, some imports will still work with a warning until a future version.
 
+To continue using the `Query` model, you must also add the `wagtail.contrib.search_promotions` application to your project's `INSTALLED_APPS` setting.
+
 #### Migration command
 
 If you have daily hits records in the `wagtailsearch.Query` you can run the management command to move these records to the new location.