Add mycelium ui to CHANGELOG.md

Signed-off-by: Lee Smet <lee.smet@hotmail.com>

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Mycelium-ui, a standalone GUI which exposes (part of) the mycelium API. This
+  does __not__ have a bundled mycelium node, so that needs to be run separately.
+
 ### Fixed
 
 - Release flow to create the Windows installer now properly extracts wintun