Add changes file for 5.5.0 release

Change-Id: I56eb43d6fe834d5fba90e78267290fd73290fd5b
Reviewed-by: Liang Qi <liang.qi@theqtcompany.com>

dist/changes-5.5.0

@@ -0,0 +1,28 @@
+Qt 5.5 introduces many new features and improvements as well as bugfixes
+over the 5.4.x series. For more details, refer to the online documentation
+included in this distribution. The documentation is also available online:
+
+  http://doc.qt.io
+
+The Qt version 5.5 series is binary compatible with the 5.4.x series.
+Applications compiled for 5.4 will continue to run with 5.5.
+
+Some of the changes listed in this file include issue tracking numbers
+corresponding to tasks in the Qt Bug Tracker:
+
+  http://bugreports.qt.io
+
+Each of these identifiers can be entered in the bug tracker to obtain more
+information about a particular change.
+
+****************************************************************************
+*                           General                                        *
+****************************************************************************
+
+- Read grayscale JPEG 2000 images as grayscale QImages
+- Fix a number of compilation warnings
+- Update bundled libwebp to version 0.4.3
+- Correctly interpret RGBA tiff images as premultiplied
+- Optional application of orientation for TIFF
+- QTBUG-38715: Build webp plugin on Android
+- Correctly read and write Grayscale8 TIFF