MFH: r439461

security/py-certbot: fix incorrect instructions in pkg-message

• Fix the example certonly command

While here, update pkg-message to cope with the renaming to "certbot"

PR: 218758
Submitted by: cpm (based on)
Reported by: Justin Clift <justin@postgresql.org>
Approved by: koobs (maintainer)

Approved by: ports-secteam (blanket)