Add a stub method to query the time zones

README.md

@@ -33,6 +33,16 @@ for KDE.
 Then running `dbus-monitor --system` as root can be used to see the
 communication between the control center and this service.
 
+Messages to the D-Bus service can also be sent with `dbus-send`. For example
+to get the list of time zones:
+
+```sh
+dbus-send --system --print-reply --type=method_call \
+  --dest=org.freedesktop.timedate1 \
+  /org/freedesktop/timedate1 \
+  org.freedesktop.timedate1.ListTimezones
+```
+
 ## Dependencies
 
 - glib