updating DIRECTORY.md

Author: cclauss

DIRECTORY.md

@@ -570,6 +570,7 @@
 
 ## [Genetic Algorithm](genetic_algorithm)
   * [Basic String](genetic_algorithm/basic_string.py)
+  * [Travelling Salesman Problem](genetic_algorithm/travelling_salesman_problem.py)
 
 ## [Geodesy](geodesy)
   * [Haversine Distance](geodesy/haversine_distance.py)