[ci skip] Docs update

Author: michalsn

user_guide_src/source/libraries/curlrequest.rst

@@ -246,8 +246,10 @@ An example::
 debug
 =====
 
-When ``debug`` is passed and set to ``true``, this will enable additional debugging to echo to STDOUT during the
-script execution. This is done by passing CURLOPT_VERBOSE and echoing the output::
+When ``debug`` is passed and set to ``true``, this will enable additional debugging to echo to STDERR during the
+script execution. This is done by passing CURLOPT_VERBOSE and echoing the output. So, when you're running a build-in
+server via ``spark serve`` you will see the output in the console. Otherwise, the output will be written to
+the server's error log.
 
 	$response->request('GET', 'http://example.com', ['debug' => true]);