address commit

https://github.com/collective/icalendar/pull/623#discussion_r1632213752

README.rst

@@ -96,7 +96,9 @@ We expect the ``master`` branch with versions ``6+`` to receive the latest updat
 Version 5
 ~~~~~~~~~
 
-Version 5 contains the ``pytz`` only
+Version 5 uses only the ``pytz`` timezone implementation, and not ``zoneinfo``.
+No updates will be released for this.
+Please use version 6 and switch to use ``pytz`` as documented above.
 
 Version 4
 ~~~~~~~~~