Adding ELI5 video (facebook#775)

Summary:
## Summary

Here at Meta Open Source, we've been creating short-form videos to explain Meta OSS projects in the simplest terms possible. We started embedding these videos into project pages as you can see in [Docusaurus home page](https://docusaurus.io/), [Jest](https://jestjs.io/), [Litho](https://fblitho.com/), [Hydra](https://hydra.cc/), etc..

Pull Request resolved: facebook#775

Test Plan: ![image](https://user-images.githubusercontent.com/12485205/154541349-c77999f1-739f-48a8-b0c0-a35c3071e7d0.png)

Reviewed By: motiz88

Differential Revision: D34306968

Pulled By: dmitryvinn-fb

fbshipit-source-id: 30f5e288671761c5a897fefd78027235e2960519

website/src/pages/index.js

@@ -81,11 +81,35 @@ const HomeSplash = () => {
   );
 };
 
+const VideoContainer = () => {
+  return (
+    <div className="container text--center margin-bottom--xl">
+      <div className="row">
+        <div className="col" style={{textAlign: 'center'}}>
+          <h2>Check it out in the intro video</h2>
+          <div>
+            <iframe
+              width="560"
+              height="315"
+              src="https://www.youtube.com/embed/E13sgMCODDk"
+              title="Explain Like I'm 5: Metro"
+              frameBorder="0"
+              allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
+              allowFullScreen
+            />
+          </div>
+        </div>
+      </div>
+    </div>
+  );
+};
+
 const Index = () => {
   return (
     <Layout title="Metro">
       <HomeSplash />
       <div className="container">
+        <VideoContainer />
         <div class="row">
           {contents.map(({content, title, image}) => {
             return (