Add warning around select_bridge hax

lib/stroke_extractor.js

@@ -332,6 +332,8 @@ function extract_stroke(paths, endpoint_map, bridge_adjacency,
     }
   }
 
+  // Here there be dragons!
+  // TODO(skishore): Document the point of the geometry in this function.
   function select_bridge(endpoint, options) {
     if (options.length === 1) {
       // Handle star-shaped strokes where one stroke ends at the intersection