The paths of many Nagios components differs by installationtype. This repository will use paths by installation from source /usr/local/nagios/. If you use Nagios installed by the paketmanager, you may need to change them to /usr/lib/nagios/.
Copy the content from commands.cfg into /usr/local/nagios/objects/commands.cfg and take care its uncommented in /usr/local/nagios/etc/nagios.cfg.
# You can specify individual object config files as shown below:
cfg_file=/usr/local/nagios/etc/objects/commands.cfg
Copy all check pi files into plugins directory.
cp check_pi_* /usr/local/nagios/libexec/
Now it could be used in any host.cfg file as the module needs.