CHANGELOG.md in jkf-0.5.0 vs CHANGELOG.md in jkf-0.5.1

@@ -5,9 +5,26 @@
 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]
 
+## [0.5.1] - 2023-06-24
+
+### Changed
+
+* Update required Ruby version to 3.0 (security fix only stable
+  version), although the library itself might works with older Ruby
+  versions.
+
+### Others
+
+* Refactor parser with StringScanner.  This makes parser approx. 5x
+  faster.
+* Fixed link to json-kifu-format
+* Remove Inch CI link on readmes
+* Lint Ruby sources
+* Add benchmark script
+
 ## [0.5.0] - 2023-06-18
 
 ### Changed
 
 * Set required Ruby version to 2.7; this will be updated to 3.0 or