Update README.md

Author: armankhondker

README.md

@@ -17,6 +17,7 @@ This repository contains free LeetCode resources to ace your coding interviews.
 - [Depth First Search](https://medium.com/basecs/deep-dive-through-a-graph-dfs-traversal-8177df5d0f13)
 - [Graph Theory](https://medium.com/basecs/a-gentle-introduction-to-graph-theory-77969829ead8)
 - [Dynaymic Programming](https://leetcode.com/discuss/general-discussion/458695/dynamic-programming-patterns)
+- [Big O Cheat Sheet](https://www.bigocheatsheet.com/) 
 
 ### [Leetcode Spaced-Repetition Template](https://docs.google.com/spreadsheets/d/1qcVCZ3VrBa2p0Tlzad0kEdG94carfZly5z81VLdz2w4/edit#gid=0)