code: func (c *Chain) Add(filter interface{}) {
  	switch filter.(type) {
  	case Filter:
  		break
  	case FilterFunc:
  		break
  	case func(*Update) bool:
  		break
  	default:
  		panic("telebot: unsupported filter type")
  	}
  
  	c.Filters = append(c.Filters, filter)
  }
docs: // Add accepts either Filter interface or FilterFunc