Add changelog

Author: xrmx

CHANGELOG.md

@@ -15,6 +15,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - `opentelemetry-instrumentation-aiohttp-client`: add support for url exclusions via `OTEL_PYTHON_EXCLUDED_URLS` / `OTEL_PYTHON_AIOHTTP_CLIENT_EXCLUDED_URLS`
   ([#3850](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3850))
+- `opentelemetry-instrumentation-httpx`: add support for url exclusions via `OTEL_PYTHON_EXCLUDED_URLS` / `OTEL_PYTHON_HTTPX_EXCLUDED_URLS`
+  ([#3837](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3837))
 
 ### Fixed