Update changelog with PR number

Author: DylanRussell

CHANGELOG.md

@@ -8,7 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Unreleased
 
 - Add `event_name` as a top level field in the `LogRecord`. Events are now simply logs with the
-`event_name` field set, the logs SDK should be used to emit events.
+`event_name` field set, the logs SDK should be used to emit events ([#4652](https://github.com/open-telemetry/opentelemetry-python/pull/4652)).
 - Update OTLP gRPC/HTTP exporters: the export timeout is now inclusive of all retries and backoffs.
   A +/-20% jitter was added to all backoffs. A pointless 32 second sleep that occurred after all retries
   had completed/failed was removed.