Improve formatting and add section for unreleased changes

CHANGELOG.md

@@ -8,6 +8,11 @@ SPDX-License-Identifier: CC-BY-4.0
 
 All notable changes will be documented in this file.
 
-## 1.0.0 (2020-04-21)
+## [Unreleased]
+
+## [1.0.0] - 2020-04-21
 
 Initial release of the workshop material.
+
+[unreleased]: https://gitlab.com/hifis/hifis-workshops/introduction-to-git-and-gitlab/workshop-material/compare/1.0.0...master
+[1.0.0]: https://gitlab.com/hifis/hifis-workshops/introduction-to-git-and-gitlab/workshop-material/-/tags/1.0.0