chore(demo): added link to caniuse for the "unsupported browsers"

Author: mfranzke

demo/index.html

@@ -82,7 +82,8 @@ <h1>
 
 			<p class="scrolling-advice">
 				Please scroll down to see these images being loaded by the polyfill on
-				unsupported browsers<span aria-hidden="true">⬇</span>
+				<a href="https://caniuse.com/loading-lazy-attr">unsupported browsers</a>
+				<span aria-hidden="true">⬇</span>
 			</p>
 		</header>