chore(functions/log_helloworld): mention var_dump (GoogleCloudPlatform#1218)

Author: Ace Nassri

functions/log_helloworld/index.php

@@ -36,6 +36,10 @@ function helloLogging(ServerRequestInterface $request): string
 
     // This doesn't log anything
     error_log('error_log does not log in Cloud Functions!');
+    
+    // For HTTP functions, this is added to the HTTP response
+    // For CloudEvent functions, this does nothing
+    var_dump('var_dump goes to HTTP response for HTTP functions');
 
     // Functions must return a String or PSR-7 Response object
     return '';