Certbot renews at 30 days remaining, so a healthy certificate never falls
below it and the old 14 day threshold could only fire after renewal had
been broken for 16 straight days, leaving 14 days to react. 25 days fires
about five days after the first failed renewal.
The script posted alerts to https://ntfy.silverwal.com/certbot, which is
served by the same nginx whose certificates it monitors. A TLS failure on
this host would make curl -fsS fail verification and drop the alert
describing that failure, leaving only a line in a log nobody reads.
ntfy is already bound to 127.0.0.1:2586, so post there instead.
These were dropped in b1b4296 when the README was trimmed, which left no
record in the repo of how the script gets onto the server or how it is
scheduled.
