Update footer!

Author: Anass Rach

_includes/nav_footer_custom.html

@@ -1 +1,8 @@
-Test footer
+<footer>
+  <p><a href="#top" id="back-to-top">Back to top</a></p>
+  <p class="text-small text-grey-dk-100" style="text-align: center; margin-top: 1rem;">
+    <a href="https://github.com/Anasss/java21docCards/tree/main" target="_blank" class="external-link">
+      Contribute or send feedback on GitHub
+    </a>
+  </p>
+</footer>