doc: User Guide

Feature set and scope, e.g.
- Device discovery: SSDP, LLDP, mDNS-SD how do they work, interfacing with Windows/macOS/Linux
- Network redundancy protocols: STP/RSTP, MRP
Configuring the system; using ifupdown2, enabling/disabling services
Diagnosing the system; using rmon, port mirroring, debugging services, searching logs
Limitations, e.g., PRP/HSR or IEEE 802.1CB will not be possible to support
Tips & Trix

document how to set up passwordless SSH

add setup wizard, based on pdmenu

setup-port script to tweak ethtool settings
setup-iface script to configure a layer-3 interface
setup-bridge script that creates a new bridge with config from cmdline
setup-firewall script that can do basic firewall rules and masquerading

split out qemu Config.in to a “make run-menuconfing”

rename qemu/ to run/, perhaps?

ship qemu/* with output/images/ for stand-alone runs of older builds