docs: Update changelog

Author: SergioGasquez

CHANGELOG.md

@@ -25,6 +25,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Allow specifying a partition label for `write-bin`, add `--partition-table`. (#828)
 - `--mmu-page-size` parameter for `flash` and `save-image` (#835)
 - Run some arguments checks for monitoring flags. (#842)
+- Add support for serial port configuration files. (#777)
 
 ### Changed