apache-airflow: add docs for additional manual testing

    ./update-providers.py

  '';

  # Note on testing the web UI:

  # You can (manually) test the web UI as follows:

  #

  #   nix shell .#python3Packages.apache-airflow

  #   airflow db init

  #   airflow reset -y # WARNING: this will wipe any existing db state you might have!

  #   airflow standalone

  #

  # Then navigate to the localhost URL using the credentials printed, try

  # triggering the 'example_bash_operator' and 'example_bash_operator' DAGs and

  # see if they report success.

  meta = with lib; {

    description = "Programmatically author, schedule and monitor data pipelines";

    homepage = "https://airflow.apache.org/";