Add link to repo from demo pages

Author: bramus

demos/src/index.html

@@ -41,6 +41,8 @@ <h1>Interop 2022 Viewport Investigation Effort Demo Pages</h1>
 
         <p>A collection of demos that allow you to debug and test the behavior of certain viewport and viewport-related aspects.</p>
 
+        <p>These demos are part of the <a href="https://github.com/web-platform-tests/interop-2022-viewport">Viewport Investigation Effort</a></p>
+
         <h2>Individual Viewports and related aspects</h2>
         <ol>
             <li><a href="individual/icb/">Initial Containing Block (ICB)</a></li>