docs: letsencrypt doesn't need additional care
    
    After commit [1] in ansible.git, it's not needed to backup
    letsencrypt certificates before moving to new box - we simply
    forget about the old cert and request new on new box.  This
    approach shouldn't cause any problems WRT quota because we only
    update the certificate regularly once per two months.
    
    [1] https://infrastructure.fedoraproject.org/cgit/ansible.git/\
        commit/?id=3cc27430b66ea166d15757ed36ff7c59b79024d0