Update CHANGELOG.md

Author: lorenzoh

CHANGELOG.md

@@ -5,7 +5,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## v0.4.0 (Unreleased)
+## v0.4.1
+
+### Added
+
+- New documentation frontend based on Pollen.jl: https://fluxml.ai/FastAI.jl/dev/i/
+- Now supports Flux.jl v0.13 (https://github.com/FluxML/FastAI.jl/pull/202)
+
+## v0.4.0 (2022-03-19)
 
 ### Added