QUICK_TEST_MAIN_WITH_SETUP: improve documentation

- Explain how the moc include works.
- Add missing Q_OBJECT macro to example.

Change-Id: I2bacdc45721bb6022f030ff4bc89c95132e35e60
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Andy Shaw <andy.shaw@qt.io>

src/qmltest/doc/src/qtquicktest-index.qdoc

@@ -181,6 +181,8 @@
 
     class Setup : public QObject
     {
+        Q_OBJECT
+
     public:
         Setup() {}
 
@@ -196,6 +198,15 @@
     #include "tst_mytest.moc"
     \endcode
 
+    The \c .moc include is based on the file name of the \c .cpp file.
+    For example, in the example above, the \c .cpp file is named
+    \c tst_mytest.cpp. If the file was named \c MyTest.cpp, the include would
+    be:
+
+    \code
+    #include "MyTest.moc"
+    \endcode
+
     \section1 Licenses
 
     Qt Quick Tests is available under commercial licenses from \l{The Qt Company}.