Add discount info to WooCommerce admin new order emails

add_action( 'woocommerce_email_after_order_table', 'add_discount_info', PHP_INT_MAX, 3 );
function add_discount_info( $_order, $sent_to_admin, $plain_text ) {
	if ( true === $sent_to_admin && 0 != $_order->get_total_discount() ) {
		echo '
' . 'Discount: ' . $_order->get_discount_to_display() . '
';
	}
}