Release notes for 0.21.0 (#521)

Author: ethangk

CHANGELOG.md

@@ -4,6 +4,12 @@ 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).
 
+## [0.21.0] - 2021-11-15
+
+- Add new rule FailwithBadUsage [@su8898]
+- Add new rule FavourReRaise [@su8898]
+- Enable running tool on .Net 6 [@Cheroukee]
+
 ## [0.20.2] - 2021-10-09
 
 - Added cyclomatic complexity rule [@davidtgillard]