Add sample custom error message.

app/lang/en/validation.php

@@ -82,7 +82,11 @@ return array(
 	|
 	*/
 
-	'custom' => array(),
+	'custom' => array(
+		'attribute-name' => array(
+			'rule-name' => 'custom-message',
+		),
+	),
 
 	/*
 	|--------------------------------------------------------------------------