Put GTP engines here.

Goban plays through external engines and ships with none of its own, so this
folder is empty on purpose. The shipped configuration expects GNU Go:

    engine/gnugo/gnugo            (or gnugo.exe on Windows)

If `gnugo` is already on your PATH there is nothing to do — the configuration
falls back to it and only the working directory is taken from `path`.

Other engines are configured in config/base.json under "bots". KataGo entries
are there and switched off; set "enabled": 1 once its binary and a model file
are in engine/katago.
