Doc: playing and pausing movies in image viewer

Change-Id: Iad73768cdb8c0a57a1b8bccd3b9fb3afe1bcbb90
Reviewed-by: Konstantin Tokarev <annulen@yandex.ru>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@nokia.com>

doc/src/howto/creator-ui.qdoc

@@ -386,6 +386,8 @@
 
         \o  Return to original size
 
+        \o  Play and pause movies
+
     \endlist
 
     \section1 Navigating with Keyboard