Certbot uses a PPA on Ubuntu 18.04. Great, I already knew what a PPA is. But why didn’t whoever wrote the documentation think it might be useful FOR THOSE WHO DO NOT KNOW WHAT THE Certbot PPA URL IS to put that information right next to the information that certbot uses a PPA?
How exactly am I supposed install Certbot when the documentation DOESN’T GIVE THE PPA URL!?!
I can see how those instructions might be unclear.
It says “Once you add it to your list of repositories all you’ll need to do is apt-get the following packages.” Then it gives a list of commands. So someone unfamiliar with apt-get might conclude that they needed to somehow find and add the PPA before going through the list of commands.
In fact (as @sahsanu pointed out) one of the commands listed is actually the one to add the PPA to your list of repositories.