This widget is no different then other custom widget. You just add the PopupPanel folder to your stemapp/widgets folder and then re-start WAB and it will be in your widget choice list.
i installed the files like you said in the correct folder but when i go to configure the widget it doesnt give me any options. shown below in image. I am using version 2.2. Is there a previous earlier version i need for popup widget that will work with 2.2. I need some additional help. Thanks
Those are the only widget configuration options. The widget will just display the popup info for what ever popup info has been defined for layers in the web map and instead of being in a popup on the map it is in the popup panel instead.