update changelog.md

Author: nkleinbaer

CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Fixed
 
+- Allow additional top-level properties on collections [#191](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/191)
 - Exclude unset fields in search response [#166](https://github.com/stac-utils/stac-fastapi-elasticsearch/issues/166)
 - Upgrade stac-fastapi to v2.4.9 [#172](https://github.com/stac-utils/stac-fastapi-elasticsearch/pull/172)
 - Set correct default filter-lang for GET /search requests [#179](https://github.com/stac-utils/stac-fastapi-elasticsearch/issues/179)