Add unreleased section to CHANGELOG post 0.5.0 release

Author: ponylang-main

CHANGELOG.md

@@ -2,6 +2,17 @@
 
 All notable changes to this project will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org/) and [Keep a CHANGELOG](http://keepachangelog.com/).
 
+## [unreleased] - unreleased
+
+### Fixed
+
+
+### Added
+
+
+### Changed
+
+
 ## [0.5.0] - 2026-05-29
 
 ### Changed