update changelog

Author: Stephan Dilly

CHANGELOG.md

@@ -13,6 +13,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Fixed
 - wrong file with same name shown in file tree ([#748](https://github.com/extrawurst/gitui/issues/748))
 
+### Internal
+- use git_repository_message [[@kosayoda](https://github.com/kosayoda)] ([#751](https://github.com/extrawurst/gitui/issues/751))
+
 ## [0.16.0] - 2021-05-28
 
 **merge branch, merge commit**