Add changes file for 5.8.0

Change-Id: I27b1252bcddd5e7e30032cd7724d348b9b06571e
Reviewed-by: Kai Koehne <kai.koehne@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Martin Smith <martin.smith@qt.io>

dist/changes-5.8.0

+Qt 5.8 introduces many new features and improvements as well as bugfixes
+over the 5.7.x series. For more details, refer to the online documentation
+included in this distribution. The documentation is also available online:
+
+  https://doc.qt.io/qt-5/
+
+The Qt version 5.8 series is binary compatible with the 5.7.x series.
+Applications compiled for 5.7 will continue to run with 5.8.
+
+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.
+
+****************************************************************************
+*                           General                                        *
+****************************************************************************
+
+  - Updated licensing information; Documentation for third-party licenses
+    used in Qt is now generated from the qt_attribution.json files in
+    each module.
+  - Updated information on supported platforms.
+  - Updated Qt for embedded Linux documentation.
+  - Updated Windows deployment tool documentation.
+  - Linked to The QML Book and more entry-level tutorials in getting
+    started documentation.
+  - Updated UI topics to discuss and link to Qt Quick Controls 2.
+  - Fixed several instances of missing, incorrect, or obsolete information.