Fix wrong example code

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

src/frequenz/dispatch/__init__.py

@@ -32,8 +32,8 @@ class Dispatcher:
         async def run():
             dispatcher = Dispatcher(API_CONNECTION_INFO)
             dispatcher.start()  # this will start the actor
-            dispatch_arrived = dispatcher.new_dispatches().new_receiver()
-            dispatch_ready = dispatcher.ready_dispatches().new_receiver()
+            dispatch_arrived = dispatcher.updated_dispatches()
+            dispatch_ready = dispatcher.ready_dispatches()
         ```
     """