Create the file /etc/xbps.d/99-xbps.hristos.net.conf with the following contents:
repository=https://xbps.hristos.net/repoThe first time you sync with this repo, you will be asked to verify the key fingerprint (see below).
10:44:2f:71:9b:c7:f3:f9:6d:ad:92:82:58:de:29:0f
linux-fsync (source)