Doc: Document that by default, QTimer is not single-shot

Change-Id: I586997ddb5ed55d68f53ddfe9302b961296cc4eb
Reviewed-by: Topi Reiniö <topi.reinio@theqtcompany.com>

src/corelib/kernel/qtimer.cpp

@@ -532,6 +532,8 @@ void QTimer::singleShot(int msec, Qt::TimerType timerType, const QObject *receiv
     A single-shot timer fires only once, non-single-shot timers fire
     every \l interval milliseconds.
 
+    The default value for this property is \c false.
+
     \sa interval, singleShot()
 */