Add step-by-step network connection debugging script

[fhunleth]

There's a set of steps that many of us are used to typing that would be good to document. It depends on the device and your host computer, though. For example, on a Mac and a Raspberry Pi Zero connected using gadget mode, we do:

1. Run ifconfig to see that a virtual Ethernet interface shows up
2. If it doesn't show up, check that you're plugged into the middle USB port on the Pi rather than the power-only port
3. If sshing to nerves.local doesn't work, look for the IP address in ifconfig and subtract 1 from the last IP address digit. Try pinging and sshing to that.
4. If sshing to the IP address works, log in. Check the mDNS configuration with MdnsLite.Info.dump_records to see what's advertised. Perhaps there's a typo.
5. If WiFi isn't working, try VintageNet.info
6. Then try VintageNetWiFi.scan to see if the network you want shows up
7. Try VintageNetWiFi.quick_configure to try configuring it again. Perhaps there was a typo in the passphrase?
8. Try ping "google.com" or weather to see if the Internet works