Update Readme.md

Author: wisdompeak

Readme.md

@@ -216,6 +216,7 @@
 [631.Design-Excel-Sum-Formula](https://github.com/wisdompeak/LeetCode/tree/master/Design/631.Design-Excel-Sum-Formula) (H) 
 [642.Design-Search-Autocomplete-System](https://github.com/wisdompeak/LeetCode/tree/master/Design/642.Design-Search-Autocomplete-System) (M+) 
 [895.Maximum-Frequency-Stack](https://github.com/wisdompeak/LeetCode/tree/master/Design/895.Maximum-Frequency-Stack) (H) 
+[1146.Snapshot-Array](https://github.com/wisdompeak/LeetCode/tree/master/Design/1146.Snapshot-Array) (H) 
 [1172.Dinner-Plate-Stacks](https://github.com/wisdompeak/LeetCode/tree/master/Design/1172.Dinner-Plate-Stacks) (H) 
 [1381.Design-a-Stack-With-Increment-Operation](https://github.com/wisdompeak/LeetCode/tree/master/Design/1381.Design-a-Stack-With-Increment-Operation) (H-) 
 [1352.Product-of-the-Last-K-Numbers](https://github.com/wisdompeak/LeetCode/tree/master/Design/1352.Product-of-the-Last-K-Numbers) (M+)