update doc

src/Facade/Payment.php

  * @package MirfalahTech\Laravel\Payment\Facade
  *
  * @method static PaymentGatewayDriver via(string $gateway = null)
+ * @method static PaymentGatewayDriver custom(string $driverClass, array $options)
  * @method static string createPaymentURL(PayableEntity $payable, array $options = [])
  * @method static bool verifyGatewayReturn(Request $request)
  * @method static bool verifyGatewayCallback(Request $request, Response &$response = null)