[WCM] [Cookbook] [Console] Improved code example about memory spooling

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | no
| Applies to    | all
| Fixed tickets | n/a

First SF2 PR, so I hope I do this right. I improved this code example a bit, because in the first place it wasn't clear to me that the flushing part should be added to instead of replacing the ``$mailer->send()`` part.