Add CHANGELOG file

CHANGELOG.md

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+# Change Log
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](http://keepachangelog.com/)
+and this project adheres to [Semantic Versioning](http://semver.org/).
+
+## [Unreleased]
+
+## [1.0.0-beta.2] - 2017-03-11
+### Added
+* Complete PHP version message
+
+### Changed
+* Refactor code architecture.
+* Use PHP version constant instead of function.
+
+### Fixed
+* Fix broken version reconciliation.
+
+## 1.0.0-beta.1 - 2017-02-21
+* Initial pre-release of whip. A package to nudge users to upgrade their software versions.
+
+[Unreleased]: https://github.com/yoast/whip/compare/1.0.0-beta.2...HEAD
+[1.0.0-beta.2]: https://github.com/yoast/whip/compare/1.0.0-beta.1...1.0.0-beta.2