Update CHANGELOG.md

Author: eldruin

CHANGELOG.md

@@ -7,7 +7,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
-- [breaking-change] Replace serial-rs with the serialport-rs crate.
+### Changed
+- [breaking-change] Replace serial-rs with the serialport-rs crate. `Serial::open` now needs a baud-rate argument as well.
 
 ## [v0.4.0-alpha.3] - 2022-08-04