Update changelog

Author: thomaseizinger

CHANGELOG.md

@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 -   Use `workflow_dispatch` instead of opening an issue as the initial trigger of the release.
 Not only is this more convenient to use, it also fixes a security vulnerability that may have allowed users without write access to execute arbitrary code within the context of the repositories GitHub action.
+-   Merge `master` in `dev` after a release branch is merged.
+Previously, we used to merge the `release` branch back into `dev`.
+However, this caused some issues because the actual merge commit was not present in the `dev` branch.
+It also prevented use of the "automatically delete head branch" feature of GitHub which works well together with the "PR retargeting" feature.
 
 ## [1.4.0] - 2020-02-22