Update CHANGELOG.md

Author: smcnab1

CHANGELOG.md

@@ -9,6 +9,18 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Added
 - ...
 
+## [Codex 2.0.0](https://github.com/UWLSimulationCentre/Codex/releases/tag/Codex-2.0.0) - 2024-01-07
+
+### Added
+- Dark Mode
+- New Item Focus
+- Re-Ordering of Items
+- Item Descriptions
+
+### Changed
+- Fixed Colouring
+- Updated Usability
+
 ## [Codex 1.0.0](https://github.com/UWLSimulationCentre/Codex/releases/tag/Codex-1.0.0) - 2023-11-26
 
 ### Added