Add changes file for Qt 5.6.3

Task-number: QTBUG-62721
Change-Id: Ibfbebdcde96ea39531f58fa12c4a7038270b1bbf
Reviewed-by: Christian Stromme <christian.stromme@qt.io>

dist/changes-5.6.3

+Qt 5.6.3 is a bug-fix release. It maintains both forward and backward
+compatibility (source and binary) with Qt 5.6.0.
+
+For more details, refer to the online documentation included in this
+distribution. The documentation is also available online:
+
+  http://doc.qt.io/qt-5/index.html
+
+The Qt version 5.6 series is binary compatible with the 5.5.x series.
+Applications compiled for 5.5 will continue to run with 5.6.
+
+Some of the changes listed in this file include issue tracking numbers
+corresponding to tasks in the Qt Bug Tracker:
+
+  https://bugreports.qt.io/
+
+Each of these identifiers can be entered in the bug tracker to obtain more
+information about a particular change.
+
+****************************************************************************
+*                          Library                                         *
+****************************************************************************
+
+ - This release contains only minor code improvements.