Add an instructions on Featured Image box of the certain Post Type

Featured Image Wordpress Insructions

/**
 * Add Instructions to Featured Image Box
 */
function ration_add_featured_image_html( $html ) {
  if( get_post_type() === 'tribe_venue' || get_post_type() === 'tribe_events' )
    $html .= '<p>Recommended dimension, 1920 x 1080.</p>';

  return $html;
}
add_filter( 'admin_post_thumbnail_html', 'ration_add_featured_image_html');