chore: rename CHANGELOG to CHANGELOG.md

And add the "Keep a Changelog" header.

Author: Schnouki

CHANGELOG renamed to CHANGELOG.md

@@ -1,3 +1,10 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
 ## Unreleased
 
 - Updates all dependenices