Go Implementation For smallest-window-in-a-string-containing-all-the-characters-of-another-string

This note is to add Go implementation of below problem
https://practice.geeksforgeeks.org/problems/smallest-window-in-a-string-containing-all-the-characters-of-another-string/0

Golang playground url : https://play.golang.org/p/ao9J2Y4veUt

Github code url