code: public function image($imageUrl, $accessibilityText = null)
      {
          $this->imageUrl = $imageUrl;
          $this->accessibilityText = $accessibilityText;
  
          return $this;
      }
docs: Set the image for a Card.
  
  @param string $imageUrl          image URL
  @param string $accessibilityText (optional) accessibility text of the image
  
  @return Dialogflow\Action\Responses\BasicCard