Add WebP guide link

Author: CrazyPython

index.html

@@ -172,7 +172,7 @@ <h3>Key</h3>
                 </td>
                 <td class=allbutie11>
                     <time>2020</time>
-                    <dt>P</dt>
+                    <dt><a href="https://developers.google.com/speed/webp/gallery1">P</a></dt>
                     <dd>WebP</dd>
                 </td>
                 <td class=chrome>