Update CHANGELOG.md

Author: achamayou

CHANGELOG.md

@@ -5,7 +5,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
-## Unreleased
+## [0.18.0]
 
 ### Changed
 
@@ -665,6 +665,7 @@ Some discrepancies with the TR remain, and are being tracked under https://githu
 
 Initial pre-release
 
+[0.18.0]: https://github.com/microsoft/CCF/releases/tag/ccf-0.18.0
 [0.17.2]: https://github.com/microsoft/CCF/releases/tag/ccf-0.17.2
 [0.17.1]: https://github.com/microsoft/CCF/releases/tag/ccf-0.17.1
 [0.17.0]: https://github.com/microsoft/CCF/releases/tag/ccf-0.17.0