out of the certbot/certbot README.rst:
> Until May 2016, Certbot was named simply letsencrypt or letsencrypt-auto, depending on install method. Instructions on the Internet, and some pieces of the software, may still refer to this older name.
Let's Encrypt creates symlink to the current keys+certs in /etc/letsencrypt/live/
It isn't very useful to copy the link targets, because they rotate with every renewal (max every 90 days, optimally every 60 days). Per default the files (key+cert) have owner root:root and 0644, which should be sufficient for synapse to read.