Add change log

Change-Id: I5646a0fba9d85f72491ff160d65607f5f01a23bc
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>

dist/changes-3.4.2.md

+Qt Creator version 3.4.2 contains bug fixes.
+
+The most important changes are listed in this document. For a complete
+list of changes, see the Git log for the Qt Creator sources that
+you can check out from the public Git repository. For example:
+
+    git clone git://code.qt.io/qt-creator/qt-creator.git
+    git log --cherry-pick --pretty=oneline v3.4.1..v3.4.2
+
+Analyzer
+
+* Fixed crash when opening context menu without data
+
+Platform Specific
+
+Windows
+
+* Added support for MSVC 2015 (QTBUG-46344)
+