Update CHANGELOG.md

Author: RobinHoutevelts

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [2.0.0-alpha3] - 2023-09-13
+### Added
+- Support `stale-while-revalidate` and `stale-if-error` cache control header
+  - [https://developer.fastly.com/learning/concepts/stale](http://web.archive.org/web/20230719193134/https://developer.fastly.com/learning/concepts/stale/)
+
 ## [2.0.0-alpha2] - 2022-06-28
 ### Fixed
 - Fix wmtwig version constraint