Update README.md

Author: akashmodak97

README.md

@@ -224,6 +224,7 @@ This repo contains some problems from different popular coding platforms like Co
 215. [Find the Pivot Integer](https://leetcode.com/problems/find-the-pivot-integer/description/)
 216. [Custom Sort String](https://leetcode.com/problems/custom-sort-string/)
 217. [Maximum Ice Cream Bars](https://leetcode.com/problems/maximum-ice-cream-bars/)
+218. [Sum In A Matrix](https://leetcode.com/problems/sum-in-a-matrix/)
 
 
 # Hacker Blocks