[Messenger] Add that the same instance of a service will be injected

Author: volendavidov

messenger.rst

@@ -707,7 +707,8 @@ you can decide to not take care of services that may leak memory.
 
 On the other hand, workers usually sequentially process messages in long-running CLI processes, which don't
 finish after processing a single message. That's why you must be careful about service
-states to prevent information and/or memory leakage.
+states to prevent information and/or memory leakage as Symfony will inject the same instance of a
+service, preserving the internal state of the service between messages.
 
 However, certain Symfony services, such as the Monolog
 :ref:`fingers crossed handler <logging-handler-fingers_crossed>`, leak by design.