code: func (api *Client) SetChannelReadMark(channelID, ts string) error {
  	return api.SetChannelReadMarkContext(context.Background(), channelID, ts)
  }
docs: // SetChannelReadMark sets the read mark of a given channel to a specific point
  // Clients should try to avoid making this call too often. When needing to mark a read position, a client should set a
  // timer before making the call. In this way, any further updates needed during the timeout will not generate extra calls
  // (just one per channel). This is useful for when reading scroll-back history, or following a busy live channel. A
  // timeout of 5 seconds is a good starting point. Be sure to flush these calls on shutdown/logout.
  // see https://api.slack.com/methods/channels.mark