The README currently doesn't include explicit instructions for users to
enable/load the systemd service - Arch Linux philosophy is that services
shouldn't autoload, so that action is required from the user. Thanks to
the very useful report from Antonio, let's fix that.

Closes: #20


Reported-by: Antonio Tigri <(@BlessedLongsword)>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>