Update applications.rst

source/applications.rst

@@ -29,6 +29,7 @@ In the **Applications** menu (Apps) section you will find Bridges, Call Block, C
   applications/follow_me.rst
   applications/gs_wave.rst
   applications/ivr.rst
+  applications/messages.rst
   applications/operator_panel.rst
   applications/phrases.rst
   applications/music_on_hold.rst