Updates the CSRF element documentation with the available options

Signed-off-by: Frank Brückner <dev@froschdesignstudio.de>

docs/book/v3/element/csrf.md

@@ -34,12 +34,14 @@ $form->add([
     'name' => 'csrf',
     'options' => [
         'csrf_options' => [
-            'timeout' => 600,
+            'timeout' => 600, // optional
         ],
     ],
 ]);
 ```
 
+All available options for the validator are listed in the [laminas-validator documentation](https://docs.laminas.dev/laminas-validator/validators/csrf/#supported-options).
+
 > ### Multiple CSRF elements must be uniquely named
 >
 > If you are using more than one form on a page, and each contains its own CSRF