Update README_EN.md

added JS solution for  2621 ,  https://leetcode.com/problems/sleep/

Author: AE-Hertz

solution/2600-2699/2621.Sleep/README_EN.md

@@ -69,6 +69,26 @@ async function sleep(millis: number): Promise<void> {
 
 <!-- tabs:end -->
 
+
+<!-- tabs:start -->
+
+#### JavaScript
+```js
+/**
+ * @param {number} millis
+ * @return {Promise}
+ */
+async function sleep(millis) {
+    return new Promise ( r => setTimeout(r,millis))
+}
+
+/** 
+ * let t = Date.now()
+ * sleep(100).then(() => console.log(Date.now() - t)) // 100
+ */
+
+<!-- tabs:end -->
+
 <!-- solution:end -->
 
 <!-- problem:end -->