Add video link for system design

pages/watch.js

@@ -37,6 +37,12 @@ const WatchList = () => (
     <div className="pt-5 pb-5 bg-light border-top">
       <div className="container">
         <div className="row">
+            <RowBlock
+              openExternal
+              title={ 'Scaling an Application' }
+              subtitle='Learn how to scale an unscalable application and how to tackle the issues in production.'
+              url='https://www.youtube.com/watch?v=a2rcgzludDU'
+            />
             <RowBlock
               openExternal
               title={ 'All about Promises in JavaScript' }