Update Readme.md

Author: wisdompeak

Readme.md

@@ -202,6 +202,7 @@
 * ``NP search`` 
 [473.Matchsticks-to-Square](https://github.com/wisdompeak/LeetCode/tree/master/DFS/473.Matchsticks-to-Square) (M+) 
 [698.Partition-to-K-Equal-Sum-Subsets](https://github.com/wisdompeak/LeetCode/tree/master/DFS/698.Partition-to-K-Equal-Sum-Subsets) (H-) 
+996.Number-of-Squareful-Arrays (H) 
 * ``memorization`` 
 [464.Can-I-Win](https://github.com/wisdompeak/LeetCode/tree/master/DFS/464.Can-I-Win) (H) 
 472.Concatenated-Words (M)