Update README.md add Leetcode section

README.md

@@ -12,3 +12,14 @@ Grad it here: [UnionFind.swift](UnionStreet/UnionFind.swift)
 # Problem
 
 **Union Find** algorithm that I often has to write from scratch myself for [Leetcode](https://leetcode.com) solutions. I have seen Union Find being implemented in a form of `struct` or `class` instead of inline functions with two arrays. This project exists so one can quickly copy-and-paste a `UnionFind` data structure to a [Swift] Leetcode solutions.
+
+# Goals
+
+1. Simple AF
+2. Tested
+
+# Leetcode
+
+Problems that *can* be solved with `Union Find` data structure.
+
+* [2709. Greatest Common Divisor Traversal](https://leetcode.com/problems/greatest-common-divisor-traversal/)