add changelog (#22)

CHANGELOG.md

@@ -0,0 +1,15 @@
+# Changelog
+
+## Unreleased
+
+- Upgrade to iRODS v4.3.3 (#16)
+- Upgrade to PostgreSQL >11 (#18)
+- Upgrade image to Ubuntu 20.04 (#19)
+- Upgrade scripts for Python3 (#21)
+- Set up logging with syslog (#16)
+- Enable setting `irods-rule-engine-plugin-python` version in `build.sh` (#27)
+- Add changelog (#22)
+
+## v4.2 (2024-01-19)
+
+- Tag release for legacy iRODS v4.2 image