Add h3 viewer (#3018)

README.md

@@ -1108,6 +1108,7 @@ _See also: [awesome-gis](https://github.com/sshuair/awesome-gis)_
 - [Bicimon](https://github.com/knrdl/bicimon) - Bike Speedometer as Progressive Web App. ([Demo](https://knrdl.github.io/bicimon/)) `MIT` `HTML5`
 - [Geo2tz](https://github.com/noandrea/geo2tz) - Get the timezone from geo coordinates (lat, lon). `MIT` `Go/Docker`
 - [GraphHopper](https://graphhopper.com/) - Fast routing library and server using OpenStreetMap. ([Source Code](https://github.com/graphhopper/graphhopper)) `Apache-2.0` `Java`
+- [H3 Viewer](https://github.com/clupasq/h3-viewer) - View/search Uber H3 (Hexagonal Hierarchical Spatial Index) cells on a map. ([Demo](https://wolf-h3-viewer.glitch.me/)) `Apache-2.0` `HTML5`
 - [Hauk](https://github.com/bilde2910/Hauk) - Easy to setup location sharing platform that lets you temporarily share your location with anyone in real-time. ([Demo](https://github.com/bilde2910/Hauk#demo-server)) `Apache-2.0` `PHP`
 - [MapBBCodeShare](https://github.com/MapBBCode/share.mapbbcode.org) - Tool for sharing custom OSM maps. Support for annotated markers, polygons, lines, multi-format import/export, multiple layers, shortlinks. ([Demo](http://share.mapbbcode.org/)) `WTFPL/Other` `PHP`
 - [Nominatim](https://nominatim.org/) - Server application for reverse geocoding (address -> coordinates) on OpenStreetMap data. ([Source Code](https://github.com/osm-search/Nominatim)) `GPL-2.0` `C`