Doc: Add information about QThread own methods thread affinity

This patch improves the documentation regarding the thread affinity of
QThread's own methods. It's not always clear for people new to threading
that a QThread object lives in the old thread were it was instantiated
and that calling the methods of said objects will also happen there.

Change-Id: I3599851ebc97a33602ca6499da254a08aec59b2b
Reviewed-by: Sze Howe Koh <szehowe.koh@gmail.com>

src/corelib/thread/qthread.cpp

@@ -219,14 +219,17 @@ QThreadPrivate::~QThreadPrivate()
     It is important to remember that a QThread instance \l{QObject#Thread
     Affinity}{lives in} the old thread that instantiated it, not in the
     new thread that calls run(). This means that all of QThread's queued
-    slots will execute in the old thread. Thus, a developer who wishes to
-    invoke slots in the new thread must use the worker-object approach; new
-    slots should not be implemented directly into a subclassed QThread.
+    slots and \l {QMetaObject::invokeMethod()}{invoked methods} will execute
+    in the old thread. Thus, a developer who wishes to invoke slots in the
+    new thread must use the worker-object approach; new slots should not be
+    implemented directly into a subclassed QThread.
 
-    When subclassing QThread, keep in mind that the constructor executes in
-    the old thread while run() executes in the new thread. If a member
-    variable is accessed from both functions, then the variable is accessed
-    from two different threads. Check that it is safe to do so.
+    Unlike queued slots or invoked methods, methods called directly on the
+    QThread object will execute in the thread that calls the method. When
+    subclassing QThread, keep in mind that the constructor executes in the
+    old thread while run() executes in the new thread. If a member variable
+    is accessed from both functions, then the variable is accessed from two
+    different threads. Check that it is safe to do so.
 
     \note Care must be taken when interacting with objects across different
     threads. See \l{Synchronizing Threads} for details.