code: func (client *Client) AddTagsToHost(host, source string, tags []string) error {
  	uri := "/v1/tags/hosts/" + host
  	if source != "" {
  		uri += "?source=" + source
  	}
  	return client.doJsonRequest("POST", uri, reqGetHostTags{Tags: tags}, nil)
  }
docs: // AddTagsToHost does exactly what it says on the tin. Given a list of tags,
  // add them to the host. The source is optionally specified, and defaults to
  // "users" as per the API documentation.