[HttpFoundation] Add StreamedResponse string iterable documentation

Author: mtarld

components/http_foundation.rst

@@ -681,8 +681,19 @@ Streaming a Response
 ~~~~~~~~~~~~~~~~~~~~
 
 The :class:`Symfony\\Component\\HttpFoundation\\StreamedResponse` class allows
-you to stream the Response back to the client. The response content is
-represented by a PHP callable instead of a string::
+you to stream the Response back to the client. The response content can be
+represented by a string iterable::
+
+    use Symfony\Component\HttpFoundation\StreamedResponse;
+
+    $chunks = ['Hello', ' World'];
+
+    $response = new StreamedResponse();
+    $response->setChunks($chunks);
+    $response->send();
+
+For most complex use cases, the response content can be instead represented by
+a PHP callable::
 
     use Symfony\Component\HttpFoundation\StreamedResponse;