v.voronoi: update manual for skeletons

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@57986 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.voronoi/v.voronoi.html

@@ -22,6 +22,13 @@ Give the centroids attributes (start with
 then optionally convert the result to a raster map with
 <em><a href="v.to.rast.html">v.to.rast</a></em>.
 
+<p>
+The extraction of skeletons and center lines with the <em>-s</em> flag 
+is a brute force appraoch. Faster and more accurate algorithms to 
+extract skeletons from areas exist but are not yet implemented. In the 
+meantime, skeletons and center lines can be simplified with the 
+Douglas-Peucker algorithm: 
+<em><a href="v.generalize.html">v.generalize method=douglas</a></em>.
 
 <h2>EXAMPLE</h2>