CHANGELOG: update for 1.0.0-alpha.6 release

Author: dlech

CHANGELOG.md

@@ -4,7 +4,7 @@ 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).
 
-## [Unreleased]
+## [1.0.0-alpha.6] - 2021-05-17
 ## Added
 - Debug option to CLI interface.
 ## Changed
@@ -49,7 +49,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Typo in `pip` arguments `README.md`.
 
 
-[Unreleased]: https://github.com/pybricks/pybricksdev/compare/v1.0.0-alpha.5..HEAD
+[Unreleased]: https://github.com/pybricks/pybricksdev/compare/v1.0.0-alpha.6..HEAD
+[1.0.0-alpha.6]: https://github.com/pybricks/pybricksdev/compare/v1.0.0-alpha.5...v1.0.0-alpha.6
 [1.0.0-alpha.5]: https://github.com/pybricks/pybricksdev/compare/v1.0.0-alpha.4...v1.0.0-alpha.5
 [1.0.0-alpha.4]: https://github.com/pybricks/pybricksdev/compare/v1.0.0-alpha.3...v1.0.0-alpha.4
 [1.0.0-alpha.3]: https://github.com/pybricks/pybricksdev/compare/v1.0.0-alpha.2...v1.0.0-alpha.3