docs: add instant navigation

Author: michalsn

docs/assets/hljs.js

@@ -1,3 +1,3 @@
-document.addEventListener('DOMContentLoaded', (ev) => {
+window.document$.subscribe(() => {
     hljs.highlightAll();
 });

mkdocs.yml

@@ -22,6 +22,8 @@ theme:
       toggle:
         icon: material/brightness-4
         name: Switch to light mode
+  features:
+    - navigation.instant
 
 extra:
   homepage: https://michalsn.github.io/codeigniter-signed-url