Update CHANGELOG.md

Author: felixhekhorn

CHANGELOG.md

@@ -4,7 +4,9 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [Unreleased](https://github.com/NNPDF/pinefarm/compare/v0.4.0...HEAD)
+
+## [0.4.0](https://github.com/NNPDF/pinefarm/compare/v0.3.3...v0.4.0) - 2025-10-29
 
 ### Added