Update changelog

Author: ja573

CHANGELOG.md

@@ -5,6 +5,8 @@ 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).
 
 ## [Unreleased]
+
+## [[0.8.9]](https://github.com/thoth-pub/thoth/releases/tag/v0.8.9) - 2022-09-21
 ### Added
   - [#426](https://github.com/thoth-pub/thoth/issues/426) - Add ProQuest Ebrary ONIX 2.1 specification
   - [#420](https://github.com/thoth-pub/thoth/issues/420) - Add RNIB Bookshare to the list of supported platforms for ONIX 2.1