code: func (b *Bundle) AddTemplateFile(filename string) *Bundle {
  	content, err := ioutil.ReadFile(filename)
  	if err != nil {
  		b.err = err
  	}
  	if b.err == nil && b.watcher != nil {
  		b.err = b.watcher.Add(filename)
  	}
  	return b.AddTemplateString(filename, string(content))
  }
docs: // AddTemplateFile adds the given soy template file text to this bundle.
  // If WatchFiles is on, it will be subsequently watched for updates.