Doc: Document signals (not handlers) under \qmlsignal

Append the handler names to the end of the corresponding signal doc.

Task-number: QTBUG-35846
Change-Id: I325cdab75ef18a19c9f29d6333039c31baa8daf6
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>

src/imports/multimedia/Video.qml

@@ -328,6 +328,8 @@ Item {
         \qmlsignal Video::paused()
 
         This signal is emitted when playback is paused.
+
+        The corresponding handler is \c onPaused.
     */
     signal paused
 
@@ -335,6 +337,8 @@ Item {
         \qmlsignal Video::stopped()
 
         This signal is emitted when playback is stopped.
+
+        The corresponding handler is \c onStopped.
     */
     signal stopped
 
@@ -342,6 +346,8 @@ Item {
         \qmlsignal Video::playing()
 
         This signal is emitted when playback is started or continued.
+
+        The corresponding handler is \c onPlaying.
     */
     signal playing