Mention Marco for demo and usage example

README.md

@@ -6,6 +6,8 @@ This module allows you to manage saved places (Points of Interest) using the [re
 
 It leverages [Geohashes](https://www.geohash.es/) to organize data, enabling efficient retrieval of places within specific geographic areas. This structure is particularly optimized for map applications that need to load data only for the visible viewport.
 
+For a demo application, as well as source code using this module, check out [Marco](https://marco.kosmos.org).
+
 ## Installation
 
 ```bash