update CHANGELOG.md

Author: RobTillaart

CHANGELOG.md

@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 
+## [0.3.1] - 2026-01-03
+- update GitHub actions
+- minor edits
+
 ## [0.3.0] - 2024-07-05
 - add **float sinusDiode(float t)**
 - add **float sinusRectified(float t)**