add note to local example about tabs/windows (#1592)

Add note to local BrowserChannel example that tabs can be in different windows. Since it shows videos for the example it isn't easy to see them being synchronized unless they're in different windows.

Co-authored-by: Philipp Hancke <[email protected]>

Author: benatkin

src/content/peerconnection/channel/index.html

@@ -48,7 +48,7 @@ <h1><a href="//webrtc.github.io/samples/" title="WebRTC samples homepage">WebRTC
         <button id="hangupButton">Hang Up</button>
     </div>
 
-    <p>Click the start button in two tabs (of the same browser) to make a call</p>
+    <p>Click the start button in two tabs (of the same browser; can be in different windows) to make a call</p>
 
     <a href="https://github.com/webrtc/samples/tree/gh-pages/src/content/peerconnection/channel"
        title="View source for this page on GitHub" id="viewSource">View source on GitHub</a>