docs: def save_image(image, filename=None):
      """
      Saves a Docker image from the remote to a local files. For performance reasons, uses the Docker command line client
      on the host, generates a gzip-tarball and downloads that.
  
      :param image: Image name or id.
      :type image: unicode
      :param filename: File name to store the local file. If not provided, will use ``<image>.tar.gz`` in the current
        working directory.
      :type filename: unicode
      """
      local_name = filename or '{0}.tar.gz'.format(image)
      cli.save_image(image, local_name)