Added poweroff

Author: ArneTR

content/en/docs/cluster/power-saving.md

@@ -61,7 +61,8 @@ In order for the shutdown to be triggered by the `client.py` you must allow the
 
 Example:
 ```bash
-echo 'ALL ALL=(ALL) NOPASSWD:/usr/bin/systemctl suspend' | sudo tee /etc/sudoers.d/green-coding-shutdown
+echo 'ALL ALL=(ALL) NOPASSWD:/usr/bin/systemctl suspend' | sudo tee /etc/sudoers.d/green-coding-shutdown # for systems that support suspend
+echo 'ALL ALL=(ALL) NOPASSWD:/usr/bin/systemctl poweroff' | sudo tee -a /etc/sudoers.d/green-coding-shutdown # for systems that only can shutdown
 sudo chmod 500 /etc/sudoers.d/green-coding-shutdown
 ```