Update changelog

Author: laurmaedje

CHANGELOG.md

@@ -5,6 +5,18 @@ 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
+
+### Added
+- New `pdfa` option for using PDF/A-compliant pdf-writer workflows.
+
+### Changed
+- Conversion is now fallible and returns a `Result`.
+- Reduce PDF sizes through better font subsetting.
+
+### Fixed
+- Fixed a bug with Unicode CMaps.
+
 ## [0.11.0]
 
 ### Added