Update CHANGELOG with new RDKit conversions

Author: hechth

CHANGELOG.md

@@ -5,10 +5,13 @@ 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
+- Added `smiles_to_inchi`, `smiles_to_inchikey`, and `inchi_to_inchikey` conversions to the RDKit converter [#179](https://github.com/RECETOX/MSMetaEnhancer/pull/179)
+
 ## [0.5.1] - 2026-05-07
 ### Added
 - Added high-level functions also for canonical smiles [#178](https://github.com/RECETOX/MSMetaEnhancer/pull/178)
-- Added `smiles_to_inchi`, `smiles_to_inchikey`, and `inchi_to_inchikey` conversions to the RDKit converter [#179](https://github.com/RECETOX/MSMetaEnhancer/pull/179)
 
 ## [0.5.0] - 2026-03-10