Add changelog

Author: pyohannes

CHANGELOG.md

@@ -37,7 +37,9 @@ release.
 - Add `user_agent.name` and `user_agent.version` attributes
   ([#452](https://github.com/open-telemetry/semantic-conventions/pull/452/))
 - Add an example for gcp_pubsub asynchronous batch publish
-  ([#545](https://github.com/open-telemetry/semantic-conventions/pull/545))
+  ([#545](https://github.com/open-telemetry/semantic-conventions/pull/545)).
+- Add messaging semantic conventions for settlement spans
+  ([#661](https://github.com/open-telemetry/semantic-conventions/pull/661)).
 
 ### Fixes