Add support for adding routes

[bensallen]

Add support for adding static routes on the macOS host via:

[network]
routes = [
  "add 192.168.102.0/24 192.168.97.8"
]

To start with, this will simply be running: route add 192.168.102.0/24 192.168.97.8. Ideally however a method to make it persistent should be found.