Add documentation for Utils namespace

Mostly so it can be linked to from the main page

Change-Id: I8bee8a0e05db9462025755782966f3a4e8ea27f9
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

src/libs/utils/utils.qdoc

@@ -0,0 +1,31 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt Creator documentation.
+**
+** 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.
+**
+****************************************************************************/
+
+/*!
+    \namespace Utils
+
+    The Utils namespace contains a collection of utility classes and functions for use by all
+    plugins.
+*/