feat: add CHANGELOG.md document to keep track of changes

Author: ar3s3ru

CHANGELOG.md

@@ -0,0 +1,29 @@
+# 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]
+### Added
+- ...
+
+### Changed
+- ...
+
+### Deprecated
+- ...
+
+### Removed
+- ...
+
+## [v0.1.0-alpha.1]
+
+A lot of changes have happened here, a lot of different API design iterations and stuff. All of which, I diligently forgot to keep track of...
+
+Sorry :)
+
+<!-- @formatter:off -->
+[Unreleased]: https://github.com/get-eventually/go-eventually/compare/v0.1.0-alpha.1..HEAD
+[v0.1.0-alpha.1]: https://github.com/get-eventually/go-eventually/compare/8bb9190..HEAD