Add a note back in that shouldn't have been deleted and try to update it for 3.0.0

Author: tleonhardt

docs/features/argument_processing.md

@@ -61,6 +61,12 @@ def do_speak(self, opts):
         self.poutput(arg)
 ```
 
+!!! note
+
+    `cmd2` sets the `prog` variable in the argument parser based on the name of the method it is decorating. This will override anything you specify in `prog` variable when creating the argument parser.
+
+    As of the 3.0.0 release, `cmd2` now sets the `prog` later than it did previously.  `prog` now gets set when the instance-specific parser deep copy is created. Previously, it was set in the `with_argparser` decorator itself.
+
 ## Help Messages
 
 By default, `cmd2` uses the docstring of the command method when a user asks for help on the