tweaked an example

doc/services.rst

@@ -159,7 +159,12 @@ using the ``protect`` method::
     // calling it now
     echo $add(2, 3);
 
-Note that the container is not provided as an argument to protected closures (but you can access it via `use($app)`).
+Note that the container is not provided as an argument to protected closures.
+However, you can inject it via `use($app)`::
+
+    $app['closure_parameter'] = $app->protect(function ($a, $b) use ($app) {
+        // ...
+    });
 
 Core services
 -------------