[gimp-macos-build] Add macOS specific changelog

[Alex Samorukov <asamorukov src gnome org>]

commit 2bd01bdee40f4cca75b9e9bb003e476db1e4c3b5
Author: Oleksii Samorukov <oleksii_samorukov mckinsey com>
Date:   Fri Nov 8 23:36:36 2019 +0100

    Add macOS specific changelog

 ChangeLog.md | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
---
diff --git a/ChangeLog.md b/ChangeLog.md
new file mode 100644
index 0000000..d353cd6
--- /dev/null
+++ b/ChangeLog.md
@@ -0,0 +1,14 @@
+## macOS specific changes
+
+### not released yet
+
+- Dependency updates: openjpeg, gexiv2, python2, lcms2, libtiff
+- Enable matting levin engine support using macOS `Accelerate` framework and SuiteSparse
+- LibHEIF updated to 1.6 to fix crash on save
+- Performance improvements in LibHEIF save due to enabled ASM in x265
+
+### gimp-2.10.14-x86_64.dmg
+
+- macOS Catalina compatibility
+- DMG opens folder with installer shortcut
+- Build is notarised (without hardened runtime so far)