Add marimo control example

Author: Stefan Kuethe

docs/concepts/controls.md

@@ -7,3 +7,14 @@ Controls are user interface elements that you can add to your map:
 ```
 
 > See [Controls API](../../api/controls/)
+
+```python {marimo display_code=True}
+import openlayers as ol
+from openlayers.basemaps import CartoBasemapLayer
+
+m = ol.MapWidget(
+    layers=[CartoBasemapLayer()],
+    controls=[ol.OverviewMapControl(collapsed=False)]
+)
+m
+```