coturn needs to be restarted after certbot updates certs

I just set up HPB and it's working great, thank you for this script.

I was looking through the config and it doesn't look like coturn gets restarted after certs get renewed certbot.
It seems the easiest way is to add the following line to ```/etc/letsencrypt/renewal/<MYDOMAIN>-rsa.conf```

```renew_hook = systemctl restart coturn.service```
