Improve docstring of CriticFactoryReuseActor

tianshou/highlevel/module/critic.py

@@ -165,6 +165,12 @@ class CriticFactoryReuseActor(CriticFactory):
     """A critic factory which reuses the actor's preprocessing component.
 
     This class is for internal use in experiment builders only.
+
+    Reuse of the actor network is supported through the concept of an actor future (:class:`ActorFuture`).
+    When the user declares that he wants to reuse the actor for the critic, we use this factory to support this,
+    but the actor does not exist yet. So the factory instead receives the future, which will eventually be filled
+    when the actor factory is called. When the creation method of this factory is eventually called, it can use the
+    then-filled actor to create the critic.
     """
 
     def __init__(self, actor_future: ActorFuture):