Add qtcore.qdoc. The QtCore main page was missing from the docs.

Change-Id: Id81f7b11302538dee9d3459b1feb0ad93c53fada
Reviewed-on: http://codereview.qt-project.org/5519
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Casper van Donderen <casper.vandonderen@nokia.com>

doc/src/core/qtcore.qdoc

@@ -0,0 +1,42 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:FDL$
+** GNU Free Documentation License
+** 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.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms
+** and conditions contained in a signed written agreement between you
+** and Nokia.
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+    \module QtCore
+    \title QtCore Module
+    \ingroup modules
+
+    \keyword QtCore
+
+    \brief The QtCore module contains core non-GUI functionality.
+
+    All other Qt modules rely on this module. To include the
+    definitions of the module's classes, use the following directive:
+
+    \snippet doc/src/snippets/code/doc_src_qtcore.cpp 0
+*/
+