Add missing comparison links for the 1.6 release

Author: samhed

CHANGELOG.md

@@ -58,7 +58,8 @@ First release.
 
 - An Ansible role to install the ThinLinc server software.
 
-[unreleased]: https://github.com/cendio/ansible-role-thinlinc-server/compare/v1.5...HEAD
+[unreleased]: https://github.com/cendio/ansible-role-thinlinc-server/compare/v1.6...HEAD
+[1.6]: https://github.com/cendio/ansible-role-thinlinc-server/compare/v1.5...v1.6
 [1.5]: https://github.com/cendio/ansible-role-thinlinc-server/compare/v1.4...v1.5
 [1.4]: https://github.com/cendio/ansible-role-thinlinc-server/compare/v1.3...v1.4
 [1.3]: https://github.com/cendio/ansible-role-thinlinc-server/compare/v1.2...v1.3