Added changelog

Author: rimi-itk

CHANGELOG.md

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+# 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/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+* [PR-13](https://github.com/OS2web/os2web_datalookup/pull/13)
+  Added support for [os2web_key](https://github.com/OS2web/os2web_key)
+
+[Unreleased]: https://github.com/itk-dev/os2web_datalookup