add support for Ubuntu 18.04
The relay guide should be ready once Ubuntu 18.04 is released (2018-04-26), this depends on #25888 (moved)
- wait for #25888 (moved) to get committed
- confirm current instructions work on Ubuntu 18.04
The relay guide should be ready once Ubuntu 18.04 is released (2018-04-26), this depends on #25888 (moved)