Added a note about disabling FastCGI buffering in Nginx

Author: javiereguiluz

components/http_foundation.rst

@@ -468,8 +468,12 @@ represented by a PHP callable instead of a string::
     you must call ``ob_flush()`` before ``flush()``.
 
     Additionally, PHP isn't the only layer that can buffer output. Your web
-    server might also buffer based on its configuration. What's more, if you
-    use FastCGI, buffering can't be disabled at all.
+    server might also buffer based on its configuration. Some servers, such as
+    Nginx, let you disable buffering at config level or adding a special HTTP
+    header in the response::
+
+        // disables FastCGI buffering in Nginx only for this response
+        $response->headers->set('X-Accel-Buffering', 'no')
 
 .. _component-http-foundation-serving-files: