Update README.md

Author: harmeetsingh11

Diff for: 2666-allow-one-function-call/README.md

@@ -1,4 +1,4 @@
-<h2><a href="https://leetcode.com/problems/allow-one-function-call/">2666. Allow One Function Call</a></h2><h3>Easy</h3><hr><div><p>Given a function <code>fn</code>, return a new function that is identical to the original function except that it ensures&nbsp;<code>fn</code>&nbsp;is&nbsp;called at most once.</p>
+<h2><a href="https://leetcode.com/problems/allow-one-function-call/">2666. Allow One Function Call</a></h2><img src="https://img.shields.io/badge/Easy-brightgreen" alt="Easy" /><hr><div><p>Given a function <code>fn</code>, return a new function that is identical to the original function except that it ensures&nbsp;<code>fn</code>&nbsp;is&nbsp;called at most once.</p>
 
 <ul>
 	<li>The first time the returned function is called, it should return the same result as&nbsp;<code>fn</code>.</li>