Doc: recommend using QVERIFY with QSignalSpy::wait, so people don't forget.

Change-Id: I63a04b64368a4b8aa6cfea88780b8dd6ba38b8bf
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>

src/testlib/doc/snippets/code/doc_src_qsignalspy.cpp

@@ -79,3 +79,7 @@ QModelIndex result = qvariant_cast<QModelIndex>(spy.at(0).at(0));
 //! [4]
 QSignalSpy spy(myPushButton, SIGNAL(clicked(bool)));
 //! [4]
+
+//! [5]
+QVERIFY(spy.wait(1000));
+//! [5]

src/testlib/qsignalspy.qdoc

@@ -94,4 +94,7 @@
     Optionally the event loop can return earlier on a \a timeout (in milliseconds).
 
     Returns true if the signal was emitted at least once in \a timeout milliseconds, otherwise returns false.
+
+    Example:
+    \snippet code/doc_src_qsignalspy.cpp 5
 */