Change section title to 'Visa Card Payment'

Updated section title from 'Virtual POS Payment' to 'Visa Card Payment' for clarity.

Author: bernard-ng

README.md

@@ -71,7 +71,7 @@ after that the payment will be processed and the callback url will be called wit
 $response = $flexpay->pay($mobile);
 ```
 
-### Virtual POS Payment
+### Visa Card Payment
 You can set up card payment via VPOS features, which is typically used for online payments.
 it's a gateway that allows you to accept payments from your customers using their credit cards.