Vere should ask user to setcap in `.run next`

[belisarius222]

If a user on Linux runs /path/to/pier/.run next and had previously run the setcap 'cap_net_bind_service=+ep' /path/to/vere command to allow the Urbit binary to bind port 80, then Vere should print a loud warning to remind the user to set it again on the new binary.

[joemfb]

It's also possible to configure linux to allow any binary to bind lower ports. It'd be good to mention this option in our docs:

sysctl net.ipv4.ip_unprivileged_port_start=80

or

echo 80 | sudo tee /proc/sys/net/ipv4/ip_unprivileged_port_start