[skip ci] update changelog

Author: infeo

CHANGELOG.md

@@ -10,7 +10,8 @@ Changes to prior versions can be found on the [Github release page](https://gith
 ## [Unreleased](https://github.com/cryptomator/cryptofs/compare/2.9.0...HEAD)
 
 ### Added
-* [changelog](CHANGELOG.md) file
+* Files-in-Use-Feature: Optional feature to indicate for external parties if a file is currently opened ([#312](https://github.com/cryptomator/cryptofs/pull/312))
+* Changelog file
 
 ### Changed
 * Use JDK 25 for build (bf26d6c9cd15a2489126ee0409a8ec9eca59da0c)