Document cjdroute.conf about docs HOT 3 OPEN

I think this commit takes care of it, but another pair of eyes would be great.

from docs.

Something might need to be added to reflect that there are two UDPInterfaces now, one for ipv6 and one for ipv4.

from docs.

Information regarding cjdroute.conf is scattered:

1. https://github.com/hyperboria/docs/blob/master/notes/cjdroute-conf.md
   • I'm considering moving this to cjdns/cjdroute-conf.md, but this might break links.
   • this goes back to the problem raised in this issue, how can we structure our documentation so as to make links less fragile?
2. https://github.com/hyperboria/docs/blob/master/cjdns/peering-over-UDP-IP.md
   • this should probably be a section in #1, but before moving it, I'd like to address the dead link issue

from docs.