This guide seems pretty straight forward, including automated renewal:
It uses apt-get and the Ubuntu PPA for installing certbot, but that's not applicable for CentOS. You can use the official certbot site for guidance on how to install certbot for CentOS: https://certbot.eff.org/lets-encrypt/centosrhel7-other
I would strongly suggest to try the snapd version, as that's probably the future way to install and maintain certbot by the development team. However, as you can see, it's also possible to use yum.
I have no experience with the certbot-zimbra script (which seems to be some kind of wrapper script around certbot to install the certificate in the right place for Zimbra?) used in that guide though. YMMV.