add comment to explain expiration date formatting

Author: samranahm

src/components/AddPaymentCard/PaymentCardForm.tsx

@@ -144,6 +144,8 @@ function PaymentCardForm({
 
     const previousValueRef = useRef<string>('');
 
+// Formats user input into a valid expiration date (MM/YY) and automatically adds slash after the month.
+// Ensures the month is always between 01 and 12 by correcting invalid value to match the proper format.
     const onChangeExpirationDate = useCallback((newValue: string) => {
         if (typeof newValue !== 'string') {
             return;