I've tried a number of times to send this through `git send-email`, but
it seems to get caught in a spam filter or similar.

Trying as attachment now.

Note that this uses 'nss-certs' for easy testing, but is intended to use
'le-certs' from this thread:

https://lists.gnu.org/archive/html/guix-devel/2017-02/msg01146.html