Update changelog

Author: rmm5t

CHANGELOG.md

@@ -1 +1,37 @@
-See [GitHub Releases](https://github.com/rmm5t/minitest-matchers_vaccine/releases)
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com//), and this project adheres to [Semantic Versioning](https://semver.org/).
+
+## [Unreleased] - TBD
+
+- Add GitHub CI workflow
+- Add Ruby 3 support
+
+## [1.0.4] - 2016-05-31
+
+- Prevent warnings for `@subject` instance variable not initialized
+
+## [1.0.3] - 2016-05-31
+
+- Improved Ruby 2.2 support (#1 thanks to @spovich).
+
+## [1.0.2] - 2016-05-31
+
+- Renamed MiniTest to Minitest
+
+## [1.0.1] - 2016-05-31
+
+- Bug fixes
+
+## [1.0.0] - 2016-05-31
+
+- Initial release
+
+[Unreleased]: https://github.com/rmm5t/minitest-matchers_vaccine/compare/v1.0.4..HEAD
+[1.0.4]: https://github.com/rmm5t/minitest-matchers_vaccine/compare/v1.0.3..v1.0.4
+[1.0.3]: https://github.com/rmm5t/minitest-matchers_vaccine/compare/v1.0.2..v1.0.3
+[1.0.2]: https://github.com/rmm5t/minitest-matchers_vaccine/compare/v1.0.1..v1.0.2
+[1.0.1]: https://github.com/rmm5t/minitest-matchers_vaccine/compare/v1.0.0..v1.0.1
+[1.0.0]: https://github.com/rmm5t/minitest-matchers_vaccine/compare/6fdef88..v1.0.0