comrade: add package

comrade: add package

Serverless peer-to-peer terminal sharing: a host shares a tmux session
that a client joins with a token, over a hole-punched link discovered on
the mainline DHT or link-local multicast, wrapped in an end-to-end SSH
session with the host key pinned in the token.

comrade adds no crypto of its own and follows whatever backend libssh
already links; OpenWrt's libssh uses mbedTLS, so this resolves to
monocypher.

Signed-off-by: Daniel Golle <redacted>