Add changes-5.1.0 file

Change-Id: I0d3ebb797ee1c185162a6defa4a58e2ffbfca41b
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

dist/changes-5.1.0

+Qt 5.1 introduces many new features and improvements as well as bugfixes
+over the 5.0.x series. For more details, refer to the online documentation
+included in this distribution. The documentation is also available online:
+
+  http://qt-project.org/doc/qt-5.1
+
+The Qt version 5.1 series is binary compatible with the 5.0.x series.
+Applications compiled for 5.0 will continue to run with 5.1.
+
+Some of the changes listed in this file include issue tracking numbers
+corresponding to tasks in the Qt Bug Tracker:
+
+  http://bugreports.qt-project.org/
+
+Each of these identifiers can be entered in the bug tracker to obtain more
+information about a particular change.
+
+****************************************************************************
+*                           General                                        *
+****************************************************************************
+
+ - This release contains only minor code improvements.