[ci skip] Add documentation for using custom validator

docs/reference/validators.rst

@@ -0,0 +1,34 @@
+.. _reference.validators:
+
+==========
+Validators
+==========
+
+.. php:namespace:: Ramsey\Uuid\Validator
+
+.. php:interface:: ValidatorInterface
+
+    .. php:method:: getPattern()
+
+        :returns: The regular expression pattern used by this validator
+        :returntype: ``string``
+
+    .. php:method:: validate($uuid)
+
+        :param string $uuid: The string to validate as a UUID
+        :returns: True if the provided string represents a UUID, false otherwise
+        :returntype: ``bool``
+
+.. php:class:: GenericValidator
+
+    Implements :php:interface:`Ramsey\\Uuid\\Validator\\ValidatorInterface`.
+
+    GenericValidator validates strings as UUIDs of any variant.
+
+.. php:namespace:: Ramsey\Uuid\Rfc4122
+
+.. php:class:: Validator
+
+    Implements :php:interface:`Ramsey\\Uuid\\Validator\\ValidatorInterface`.
+
+    Rfc4122\Validator validates strings as UUIDs of the RFC 4122 variant.