README: add note about tests

Stunkymonkey · Stunkymonkey · commit f65af22d1f32 · 2025-04-22T23:17:06.000+02:00
diff --git a/README.md b/README.md
@@ -11,6 +11,7 @@ based on [related work](https://ad-publications.cs.uni-freiburg.de/GIS_personal_
 ```bash
 git submodule update --init --recursive
 cargo build --release
+cargo test --release
 ```
 
 ## Extract OSM-data
