added docblock and readme docs for using the new filter

README.md

@@ -109,6 +109,40 @@ V::lang('ar');
  * `dateBefore` - Field is a valid date and is before the given date
  * `dateAfter` - Field is a valid date and is after the given date
  * `contains` - Field is a string and contains the given string
+ * `creditCard` - Field is a valid credit card number
+
+ ## Credit Card Validation usage
+
+ Credit card validation currently allows you to validate a Visa `visa`,
+ Mastercard `mastercard`, Dinersclub `dinersclub`, American Express `amex`
+ or Discovery `discovery`
+
+ This will check the credit card against each card type
+```php
+$v->rule('creditCard', 'credit_card');
+```
+
+To optionally filter card types, add the slug to an array as the next parameter:
+
+```php
+$v->rule('creditCard', 'credit_card', ['visa', 'mastercard']);
+```
+
+If you only want to validate one type of card, put it as a string:
+
+```php
+$v->rule('creditCard', 'credit_card', 'visa');
+```
+
+If the card type information is coming from the client, you might also want to
+still specify an array of valid card types:
+
+```php
+$cardType = 'amex';
+$v->rule('creditCard', 'credit_card', $cardType, ['visa', 'mastercard']);
+$v->validate(); // false
+```
+
 
 ## Adding Custom Validation Rules
 

src/Valitron/Validator.php

@@ -472,6 +472,15 @@ class Validator
         return (is_bool($value)) ? true : false;
     }
 
+    /**
+     * Validate that a field contains a valid credit card
+     * optionally filtered by an array
+     *
+     * @param string  $field
+     * @param string $value
+     * @param array $params
+     * @return bool
+     */
     protected function validateCreditCard($field, $value, $params)
     {
         /**