Update TODO.txt

Author: VHRanger

TODO.txt

@@ -4,6 +4,8 @@ Add GGVec negative_lr_ratio parameter
 
 Harden n2v walks to dead end nodes like in regular random walks
 
+Improve n2v walks speed like in here: https://github.com/louisabraham/fastnode2vec
+
 self.names EVERYWHERE!
     Fix segfault in node2vec
     Fix node2vec walk names mapping (should use csrgraphs natively)