Add changes file for Qt 5.12.1

+ f611299f Doc: Get rid of QT_INSTALL_HEADERS in documentation config
+ 16d33f91 Bump version
+ 92f9b785 Bump version
+ 328418b0 QAndroidIntent::putExtra: Fix JNI return value syntax
+ 48256a15

 Bump version

Change-Id: I11a8e7e46809fbffbc1777126d5fd171a9f76b74
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

dist/changes-5.12.1

+Qt 5.12.1 is a bug-fix release. It maintains both forward and backward
+compatibility (source and binary) with Qt 5.12.0.
+
+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 5.12 series is binary compatible with the 5.11.x series.
+Applications compiled for 5.11 will continue to run with 5.12.
+
+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.
+
+ - This release contains only minor code improvements.