[HttpFoundation] Add a doc entry since Response's methods now accept immutable object

Author: Simperfit

components/http_foundation.rst

@@ -400,13 +400,15 @@ of methods to manipulate the HTTP headers related to the cache:
 * :method:`Symfony\\Component\\HttpFoundation\\Response::setEtag`;
 * :method:`Symfony\\Component\\HttpFoundation\\Response::setVary`;
 
+The methods :method:`Symfony\\Component\\HttpFoundation\\Response::setExpires`, :method:`Symfony\\Component\\HttpFoundation\\Response::setLastModified` and :method:`Symfony\\Component\\HttpFoundation\\Response::setData` accepts an immutable date object.
+
 The :method:`Symfony\\Component\\HttpFoundation\\Response::setCache` method
 can be used to set the most commonly used cache information in one method
 call::
 
     $response->setCache(array(
         'etag'          => 'abcdef',
-        'last_modified' => new \DateTime(),
+        'last_modified' => new \DateTime(), // Any object implementing \DateTimeInterface
         'max_age'       => 600,
         's_maxage'      => 600,
         'private'       => false,