readme: Autorun example

[second-constantine]

Create a simple systemd unit (for autorun)

# Copy pi400kb
sudo cp pi400kb /usr/sbin/pi400kb

# Create unit
sudo systemctl edit --force --full how_keyboard.service

And add

[Unit]
Description=simple unit for user pi400 how keyboard

[Service]
ExecStart=/usr/sbin/pi400kb
User=root   
Group=root   
Type=simple
Restart=on-failure

[Install]
WantedBy=multi-user.target

Try and enable service

# start
sudo systemctl start how_keyboard.service
# check status
sudo systemctl status how_keyboard.service
# enable autorun if it's ok
sudo systemctl enable how_keyboard.service

[Gadgetoid]

sudo systemctl edit --force --full how_keyboard.service

Today I learned!

We could probably include the systemd unit file in the repository.

[rolandog]

We should also probably mention that libcomposite should be added to /etc/modules (might resolve #39):

echo 'libcomposite' | sudo tee -a /etc/modules