Update CHANGELOG for v0.2.x release

This release introduces a major API change to support browser environments and enable future JSZip migration. All processor methods are now asynchronous and return Promises.

Author: willwade

CHANGELOG.md

@@ -5,7 +5,7 @@ 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).
 
-## [Unreleased]
+## v0.2.x
 
 ### 🔄 BREAKING CHANGE - Async API Migration