Oh, it is there! It is a very short part, so it is easy to miss:
Let's Encrypt, once again!
Now we will run certbot --apache again, to generate a certificate for our second domain. You can follow the instructions from the previous article. There is no reason to copy/paste them here, as it will get ridiculously long!
Anyway, if you set a certificate for a vhost once, if you have the auto-renew configured (as shown in the previous part), it will auto-renew it!