Add 0.9.1 to CHANGELOG

Ref. eng/recordflux/RecordFlux#1302

CHANGELOG.md

@@ -5,11 +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]
-
-### Added
-
-- User's Guide (#223)
+## [0.9.1] - 2023-03-28
 
 ### Fixed
 
@@ -355,7 +351,7 @@ Improvements:
 
 ## [0.1.0] - 2019-05-14
 
-[unreleased]: https://github.com/AdaCore/RecordFlux/compare/v0.9.0...HEAD
+[0.9.1]: https://github.com/AdaCore/RecordFlux/compare/v0.9.0...v0.9.1
 [0.9.0]: https://github.com/AdaCore/RecordFlux/compare/v0.8.0...v0.9.0
 [0.8.0]: https://github.com/AdaCore/RecordFlux/compare/v0.7.1...v0.8.0
 [0.7.1]: https://github.com/AdaCore/RecordFlux/compare/v0.7.0...v0.7.1