Add 'Qt Core Changes in Qt 6'

Skeleton to document changes to Qt Core in Qt 6.

Task-number: QTBUG-71036
Task-number: QTBUG-84051
Change-Id: I2720beffb934121258331efd9eeb91c07d40a5bf
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/corelib/doc/src/qt6-changes.qdoc

@@ -0,0 +1,41 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:FDL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Free Documentation License Usage
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of
+** this file. Please review the following information to ensure
+** the GNU Free Documentation License version 1.3 requirements
+** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+    \page qtcore-changes-qt6.html
+    \title Porting to Qt 6 - Qt Core
+
+    Qt 6 is a result of the conscious effort to make the framework more
+    efficient and easy to use.
+
+    We try to maintain binary and source compatibility for all the public
+    APIs in each release. But some changes were inevitable in an effort to
+    make Qt a better framework.
+
+    In this topic we summarize those changes in Qt Core, and provide guidance
+    to handle them.
+*/

src/corelib/doc/src/qtcore-index.qdoc

@@ -102,6 +102,11 @@
     \li \l{The Event System}
     \endlist
 
+    \section1 Module Evolution
+
+    \l{Porting to Qt 6 - Qt Core} lists important changes in the module API
+    and functionality that were done for the Qt 6 series of Qt.
+
     \section1 Licenses and Attributions
 
     Qt Core is available under commercial licenses from \l{The Qt Company}.