Changelog: add release 2.1.5

[atomist:generated] [atomist-skill:atomist/keep-a-changelog-skill]

Author: atomist-bot

CHANGELOG.md

@@ -5,7 +5,9 @@ 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](https://github.com/atomist/sdm/compare/2.1.4...HEAD)
+## [Unreleased](https://github.com/atomist/sdm/compare/2.1.5...HEAD)
+
+## [2.1.5](https://github.com/atomist/sdm/compare/2.1.4...2.1.5) - 2021-06-03
 
 ### Added