added a sentence about the HttpException::setHeaders method

Author: smatyas

components/http_kernel/introduction.rst

@@ -560,7 +560,9 @@ below for more details).
        then ``getStatusCode`` and ``getHeaders`` are called on the exception
        and used to populate the headers and status code of the ``FlattenException``
        object. The idea is that these are used in the next step when creating
-       the final response.
+       the final response. If you want to set custom HTTP headers, you can always
+       use the ``setHeaders`` method on exceptions derived from the
+       :class:`Symfony\\Component\\HttpKernel\\Exception\\HttpException` class.
 
     3) A controller is executed and passed the flattened exception. The exact
        controller to render is passed as a constructor argument to this listener.
@@ -595,7 +597,7 @@ each event has their own event object:
 =====================  ================================  ===================================================================================
 Name                   ``KernelEvents`` Constant         Argument passed to the listener
 =====================  ================================  ===================================================================================
-kernel.request         ``KernelEvents::REQUEST``         :class:`Symfony\\Component\\HttpKernel\\Event\\GetResponseEvent`                    
+kernel.request         ``KernelEvents::REQUEST``         :class:`Symfony\\Component\\HttpKernel\\Event\\GetResponseEvent`
 kernel.controller      ``KernelEvents::CONTROLLER``      :class:`Symfony\\Component\\HttpKernel\\Event\\FilterControllerEvent`
 kernel.view            ``KernelEvents::VIEW``            :class:`Symfony\\Component\\HttpKernel\\Event\\GetResponseForControllerResultEvent`
 kernel.response        ``KernelEvents::RESPONSE``        :class:`Symfony\\Component\\HttpKernel\\Event\\FilterResponseEvent`