To setup Pushover notifications, you need to first login to Pushover. Once there, you will see your user key. Paste this into your user key and you're good to go.
If you wish to send notifications to a 'group', scroll down to 'your groups', select the group you wish to post the notification to, select it, and paste the key in there
Please note:
ONLY group or user key is used at this time. Both will not work.