docs: def build_agency(pfeed):
      """
      Given a ProtoFeed, return a DataFrame representing ``agency.txt``
      """
      return pd.DataFrame({
        'agency_name': pfeed.meta['agency_name'].iat[0],
        'agency_url': pfeed.meta['agency_url'].iat[0],
        'agency_timezone': pfeed.meta['agency_timezone'].iat[0],
      }, index=[0])