Add docs to README for UuidFilter

Author: chadicus

README.md

@@ -152,6 +152,20 @@ $value = '{ "string": "value", "array": [1, 2, 3] }';
 assert($value === ['string' => 'value', 'array' => [1, 2, 3]]);
 ```
 
+#### UuidFilter::filter
+
+This filter verifies a given string is a valid universally unique identifier.
+
+The second parameter can be set to `true` to allow null values through without an error.
+
+The third parameter determines which UUID version the value will be validated against. By default, the filter will succeed if the values matches version 1, 4, or 7
+
+```php
+$value = '1a42403c-a29d-11ef-b864-0242ac120002';
+$filtered = \TraderInteractive\Filter\UuidFilter::filter($value);
+assert($value === $filtered);
+```
+
 #### XmlFilter::filter
 
 This filter ensures the given string is valid XML.