simpler geo label example (#1660)

Co-authored-by: Philippe Rivière <[email protected]>

Author: mbostock

docs/transforms/centroid.md

@@ -33,7 +33,7 @@ Plot.plot({
 ```
 :::
 
-Also fun, we can pass the centroid to the [voronoi mark](../marks/delaunay.md).
+For fun, we can pass county centroids to the [voronoi mark](../marks/delaunay.md).
 
 :::plot defer https://observablehq.com/@observablehq/plot-centroid-voronoi
 ```js