feat: add changelog (#40)

CHANGELOG.md

@@ -0,0 +1,23 @@
+# 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]
+
+## [0.0.9]
+
+### Added
+
+- Started Changelog
+
+### Changed
+
+- Switch validate command line options from filepaths to boolean options
+- Validate all `.tf` files in directory of documentation input file rather than
+only validating specified variables/output files
+
+[unreleased]: https://github.com/mineiros-io/terradoc/compare/v0.0.9...HEAD
+[0.0.9]: https://github.com/mineiros-io/terradoc/compare/v0.0.8...v0.0.9