docs: def expand(conf, output_requirements_filename, input_requirements_filename):
      """Expand given requirements file by extending it using pip freeze
  
      args:
  
      input_requirements_filename: the requirements filename to expand
  
      output_requirements_filename: the output filename for the expanded
      requirements file
      """
      exit_if_file_not_exists(input_requirements_filename, conf)
      cireqs.expand_requirements(
          requirements_filename=input_requirements_filename,
          expanded_requirements_filename=output_requirements_filename,
          **conf._asdict()
      )
      click.echo(click.style('✓', fg='green') + " {} has been expanded into {}".format(
          input_requirements_filename, output_requirements_filename
      ))