Fix doctest

         ...     def setup(self, add_arg):
         ...         add_arg("-t", "--tz", help="timezone e.g. PST")
         ...     def run(self, stdin, log):
-        ...         print(self.tz)
+        ...         print(f"Hello from {self.tz}")
         >>> try:
         ...     main("-t", "CET")
         ... except SystemExit:
         ...     print("exited cleanly")
-        CET
+        Hello from CET
         exited cleanly
 
     """