code: func (c *Callbacks) OnCUserMessageAchievementEvent(fn func(*dota.CUserMessageAchievementEvent) error) {
  	c.onCUserMessageAchievementEvent = append(c.onCUserMessageAchievementEvent, fn)
  }
docs: // OnCUserMessageAchievementEvent registers a callback for EBaseUserMessages_UM_AchievementEvent