added a comment about crossing edges in large trees

Author: mheilman

util/template_visualize_rst_tree.html

@@ -61,7 +61,7 @@
 
   tree.numLeaves = 0;
   if ( !tree.children ) {
-    tree.numLeaves = 1;
+    tree.numLeaves = 1;  // count self as a leaf
   }
 
   for (idx in tree.children) {

util/visualize_rst_tree.py

@@ -10,6 +10,10 @@
 
 For the D3.js license, see LICENSE_d3.txt or
 https://github.com/mbostock/d3/blob/master/LICENSE for the D3.js license.
+
+Note: on very large trees, edges may cross.  This appears to be a feature of
+the layout algorithm.  It could be avoided by having curved edges, but I don't
+think functionality for computing the necessary paths is available.
 '''
 
 import argparse