release: update release notes for 0.3.1

I forgot to do this when I bumped the version number.

Author: martinvonz

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.3.1] - 2022-03-13
+
 ### Fixed bugs
 
  - (#131) Fixed crash when `core.excludesFile` pointed to non-existent file, and