Add information about the query search string when creating custom controllers

Author: maartendekeizer

src/Autocomplete/src/Resources/doc/index.rst

@@ -483,6 +483,8 @@ a :ref:`custom autocompleter <custom-autocompleter>`:
     Once you have this, generate the URL to your controller and
     pass it to the ``url`` value of the ``stimulus_controller()`` Twig
     function, or to the ``autocomplete_url`` option of your form field.
+    The search term entered by the user is passed a query parameter:
+    ``query``
 
 Beyond ``url``, the Stimulus controller has various other values,
 including ``tomSelectOptions``. See the `controller.ts`_ file for