code: func FnPull(client *docker.Client, opts *BuildOptions) (err error) {
  	repo, tag := parseDockerImage(opts.GetImageName())
  	err = client.PullImage(docker.PullImageOptions{
  		Repository: repo,
  		Tag:        tag,
  	}, opts.Auth)
  	return
  }
docs: // FnPull pull image from registry