bug#75450: tor-onion-service-configuration example in Guix Manual does not work

[Vitor Hugo via Bug reports for GNU Guix]

Below follows a piece of code snippet that fixes the issue:

```
            (service tor-service-type)
            (simple-service 'my-extra-onion-service tor-service-type
                            (list (tor-onion-service-configuration
                                    (name "extra-onion-service")
                                    (mapping '((80 "127.0.0.1:8080")))))))
```

It seems that the code does not actually expect an alist.
Do I submit a change to the documentation?

Best regards,

Vitor Hugo