Update http_cache.rst - hint at whitelisting 127.0.0.1 if using HTTP Cache solution

doc/providers/http_cache.rst

@@ -54,17 +54,28 @@ setting Response HTTP cache headers::
 .. tip::
 
     If you want Silex to trust the ``X-Forwarded-For*`` headers from your
-    reverse proxy at address $ip, you will need to run your application like
-    this::
+    reverse proxy at address $ip, you will need to whitelist it as documented
+    in `Trusting Proxies
+    <http://symfony.com/doc/current/components/http_foundation/trusting_proxies.html>`_.
 
-        use Symfony\Component\HttpFoundation\Request;
+    If you would be running Varnish in front of your application on the same machine:
+    
+    .. code-block:: php
 
-        Request::setTrustedProxies(array($ip));
+        use Symfony\Component\HttpFoundation\Request;
+        
+        Request::setTrustedProxies(array('127.0.0.1', '::1'));
         $app->run();
 
 This provider allows you to use the Symfony2 reverse proxy natively with
-Silex applications by using the ``http_cache`` service::
+Silex applications by using the ``http_cache`` service. The Symfony2 reverse proxy
+acts much like any other proxy would, so you will want to whitelist it:
+
+.. code-block:: php
 
+    use Symfony\Component\HttpFoundation\Request;
+        
+    Request::setTrustedProxies(array('127.0.0.1'));
     $app['http_cache']->run();
 
 The provider also provides ESI support::