update changelog

Author: Stephan Dilly

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Added
+- `[w]` key to toggle between staging/workdir [[@terhechte](https://github.com/terhechte)] ([#595](https://github.com/extrawurst/gitui/issues/595))
+
 ### Fixed
 - push branch to its tracking remote ([#597](https://github.com/extrawurst/gitui/issues/597))