ENH: surfaceFeatureExtractDict: add comment

applications/utilities/surface/surfaceFeatureExtract/surfaceFeatureExtractDict

@@ -74,6 +74,10 @@ surface2.nas
     {
         // Add (without merging) another extendedFeatureEdgeMesh
         name                axZ.extendedFeatureEdgeMesh;
+
+        // Optionally flip features (invert all normals, making
+        // convex<->concave etc)
+        //flip                false;
     }
 
     // Output the curvature of the surface