add changelog entry

Author: MikeGoldsmith

CHANGELOG.md

@@ -13,6 +13,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Add AGENTS.md file
+  ([#4250](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4250))
 - Add Python 3.14 support
   ([#4193](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4193))
 - `opentelemetry-instrumentation-asgi`: Add exemplars for `http.server.request.duration` and `http.server.duration` metrics