add copyright notice

public/index.php

@@ -254,6 +254,11 @@ $placeholder = Filter::plural($totalPages, [sprintf(_('Over %s page or enter the
     </main>
     <!-- css animation : end -->
     <footer>
+      <!-- This product released under the MIT License (https://github.com/d47081/YGGo/blob/main/LICENSE)
+           Before removing the copyright,
+           please, make a small donation to the project contributors:
+           https://github.com/d47081/YGGo#donate-to-contributors
+      -->
       <a href="https://github.com/d47081/YGGo/issues"><?php echo _('meow') ?></a>
     </footer>
   </body>