Both commands already existed in commands/device.py but had no entry in
the README's command reference table, so users had no way to discover
them (reported as "missing"). Add rows under Advanced Configuration
explaining that mode controls how many bytes of each hop's node ID are
stored per hop in advertised/logged paths (bytes per hop = mode + 1),
matching the plen >> 6 / hash_mode + 1 logic in reader.py and
commands/base.py.
Fixes#84
