Got the demo up and running.

I've been using leaflet for my map tiling and it just works. The advantage of promomaps being offline is great.

So, now... how does one add their own POI's, routes, polygons??

1) If your information belongs in OpenStreetMap, you can add it via an editor like the web editor at https://openstreetmap.org - this will also benefit all other OSM users. You can then "refresh" your Protomaps download to get a new map.

2) If there isn't many point and polygons, it may sense to add them as Leaflet layers, especially if you want them to be interactive

3) Other options are creating vector tiles of your own data and merging or displaying them in the renderer (https://github.com/mapbox/tippecanoe is a great tool to do this from GeoJSON) but I don't have much to support this yet.