add http.cat reference

templates/404.html

@@ -31,6 +31,13 @@
         {{/onion}}
       </ul>
 
+      <img
+        src="https://http.cat/404"
+        style="width: 60%; margin: auto; display: block"
+        alt="Chat perdu"
+        loading="lazy"
+      />
+
       {{/data}}
     </main>
   </body>