Fix install instruction

and add my key to the trust db so that Debian can verify the packets,

update the repository data and install net2o, so enter:

    sudo su -

    sudo -s

    cat >/etc/apt/sources.list.d/net2o.list <<EOF

    deb [arch=i386,amd64,armhf,armel,arm64,powerpc,mips.mipsel,all] https://net2o.de/debian testing main

    deb [arch=i386,amd64,armhf,armel,arm64,powerpc,mips,mipsel,all] https://net2o.de/debian testing main

    EOF

    wget -O - https://net2o.de/bernd@net2o.de-yubikey.pgp.asc | apt-key add -

    aptitude update

    aptitude install net2o-gui

    exit

Remove the architectures on the list above which you don't need; on

Debian testing, the list is not necessary, on older versions, the all

part is not searched if you don't have that list, then Gforth fails to

install the gforth-common part.

    wget -O - https://net2o.de/bernd@net2o.de-yubikey.pgp.asc | apt-key add -

    apt update

    apt install net2o-gui

    exit

There are actually three repositories: stable, testing and unstable; at the

moment, all packages are the same; when net2o matures, stable/testing/unstable

will get different roles, just like Debian (stable=old and rusted, testing=new