updated CHANGELOG.

CHANGELOG.md

@@ -5,13 +5,15 @@ 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]
+## [0.31.0] - 2024-01-31
 
 ### Added
 - Basic BWT for sub-sequence count and offset for sequence alignment. Only supports exact matches for now.
 - Moved `BWT`, `align`, and `mash` packages to new `search` sub-directory.
 - Implemented Run-Length Burrows Wheeler Transform.
 
+[0.31.0]: https://github.com/TimothyStiles/poly/releases/tag/v0.31.0
+
 
 ## [0.30.0] - 2023-12-18
 Oops, we weren't keeping a changelog before this tag!