update readme

README.md

@@ -44,7 +44,7 @@ $gateway = Omnipay::create('Sberbank');
 $gateway->authorize(
     [
        'orderNumber' => $localOrderNumber, // local order number
-       'amount' => $order_amount, // The amount of payment (you can use integer, decimal with 2 precisions or string equal to decimal
+       'amount' => $order_amount, // The amount of payment (you can use decimal with 2 precisions for copecs or string equal to decimal)
        'returnUrl' => $callback_url // succesfull callback url
     ]
 );