add note about ->toStream()

Author: henrikac

http_client.rst

@@ -1013,6 +1013,10 @@ following methods::
     // returns detailed logs about the requests and responses of the HTTP transaction
     $httpLogs = $response->getInfo('debug');
 
+.. note::
+
+    ``$response->toStream()`` is part of :class:`Symfony\\Component\\HttpClient\\Response\\StreamableInterface`.
+
 .. note::
 
     ``$response->getInfo()`` is non-blocking: it returns *live* information