code: func NewPremailerFromFile(filename string, options *Options) (Premailer, error) {
  	fd, err := os.Open(filename)
  	if err != nil {
  		return nil, err
  	}
  	defer fd.Close()
  	d, err := goquery.NewDocumentFromReader(fd)
  	if err != nil {
  		return nil, err
  	}
  	return NewPremailer(d, options), nil
  }
docs: // NewPremailerFromFile take an filename
  // Read the content of this file
  // and create a goquery.Document
  // and then create and Premailer instance.