added new external editor feature in changes (closes #46)

Author: Stephan Dilly

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - core homebrew [formulae](https://formulae.brew.sh/formula/gitui#default): `brew install gitui` [[@vladimyr](https://github.com/vladimyr)] ([#137](https://github.com/extrawurst/gitui/issues/137))
 - show file sizes and delta on binary files diff ([#141](https://github.com/extrawurst/gitui/issues/141))
+- external editor support for commit messages [[@jonstodle](https://github.com/jonstodle)] (see ([#46](https://github.com/extrawurst/gitui/issues/46)))
 
 ### Changed
 - use terminal blue as default selection background ([#129](https://github.com/extrawurst/gitui/issues/129))