Onboard first-time macOS users

[forthrin]

Assume this is related to privileges, but README lacks instructions for macOS.

$ bandwhich 
Error: 

lo0: No such file or directory (os error 2)
en0: No such file or directory (os error 2)
awdl0: No such file or directory (os error 2)
llw0: No such file or directory (os error 2)
utun0: No such file or directory (os error 2)
utun1: No such file or directory (os error 2)
utun2: No such file or directory (os error 2)
utun3: No such file or directory (os error 2)

Also, the situation could be handled more gracefully, which is a perfect opportunity to present exact said instructions.

$ bandwhich 
bandwhich needs system privileges. Add foobar to /etc/group or bazqux to whatever.
$