updates changelog

Author: Bennett Patrick Brixen

CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Changed
 
 - Updated stac-fastapi parent libraries to v6.0.0 [#291](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/291)
+- Updated documentation to reflect use of ES environment variables
 
 ## [v5.0.0] - 2025-06-11