Add a changelog entry

Author: jpmelos

CHANGELOG.md

@@ -21,6 +21,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#212](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/212))
 - `opentelemetry-instrumentation-fastapi` Added support for excluding some routes with env var `OTEL_PYTHON_FASTAPI_EXCLUDED_URLS`
   ([#237](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/237))
+- `opentelemetry-instrumentation-flask` Do not emit a warning message for request contexts created with `app.test_request_context` or manually.
+  ([#253](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/253))
 - `opentelemetry-instrumentation-starlette` Added support for excluding some routes with env var `OTEL_PYTHON_STARLETTE_EXCLUDED_URLS`
   ([#237](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/237))
 - Add Prometheus Remote Write Exporter integration tests in opentelemetry-docker-tests