add sleep function - making delays in async functions

snippets/sleep.md

@@ -0,0 +1,12 @@
+### Sleep
+
+If you have an async function and you want to delay executing part of it. you can put your async function to sleep(in miliseconds).
+
+```js
+const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
+// async function sleepyWork() {
+//   console.log('I\'m going to sleep for 1 second.');
+//   await sleep(1000);
+//   console.log('I woke up after 1 second.');
+// }
+```