Update index.rst

Author: seb-jean

src/Turbo/doc/index.rst

@@ -838,7 +838,9 @@ created, modified or deleted:
     {% endblock %}
 
 By convention, Symfony UX Turbo will look for a template named
-``templates/broadcast/{ClassName}.stream.html.twig``. This template can contain 3 blocks: ``create`` block for entity creation. ``update`` block for entity update. ``remove`` block for entity deletion.
+``templates/broadcast/{ClassName}.stream.html.twig``. This template
+**must** contain at least 3 blocks: ``create``, ``update`` and
+``remove`` (they can be empty, but they must exist).
 
 
 Every time an entity marked with the ``Broadcast`` attribute changes,