[BUG] additional configuration instructions needed in docs/guides/airflow.md

[merobi-hub]

It appears that, to work, this guide requires much more configuration than the instructions explain. For example, port 8080 is required by both Airflow and Marquez, but no workaround is provided.

Currently, if you follow the instructions in the guide, the proxy is not receiving any events.

See also: https://github.com/OpenLineage/docs/pull/185