Add CHANGELOG and prep for release

Signed-off-by: Jakub Sztandera <[email protected]>

CHANGELOG.md

@@ -0,0 +1,25 @@
+# Changelog
+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]
+<!--
+### Added
+### Changed
+### Deprecated
+### Removed
+### Fixed
+### Security
+-->
+
+## [0.2.2] - 2020-11-06
+### Added 
+- CHANGELOG.md file
+- SECURITY.md with instructions on how to report security issues.
+- Optimized decode/encode workflow by 42%
+
+[Unreleased]: https://github.com/filecoin-project/go-bitfield/compare/v0.2.2...HEAD
+[0.2.2]: https://github.com/filecoin-project/go-bitfield/compare/v0.2.1...v0.2.2 
+