Add missing comment from codelab instructions

The comment mentioned in the codelab was missing.

See webrtc#3 for details

Author: ErikHellman

public/app.js

@@ -37,6 +37,10 @@ async function createRoom() {
 
   registerPeerConnectionListeners();
 
+  // Add code for creating a room here
+  
+  // Code for creating room above
+  
   localStream.getTracks().forEach(track => {
     peerConnection.addTrack(track, localStream);
   });