fixup! improve changelog template

Author: jonasnick

doc/CHANGELOG.md

@@ -1,5 +1,12 @@
+# Changelog
+
 This file is currently only a template for future use.
 
-# MAJOR.MINOR.PATCH - YYYY-MM-DD
+Each change falls into one of the following categories: Added, Changed, Deprecated, Removed, Fixed or Security.
+
+## [Unreleased]
+
+## [MAJOR.MINOR.PATCH] - YYYY-MM-DD
 
-- [Link to Pull Request](https://link-to-pr)
+### Added/Changed/Deprecated/Removed/Fixed/Security
+- [Title with link to Pull Request](https://link-to-pr)