Attribute source of accessible navigation toggle script

src/_includes/global/navbar.njk

@@ -89,6 +89,8 @@
 </style>
 
 <script defer>
+    {# Accessible hamburger menu navigation script based on:
+    https://accessibleweb.dev/navigation #}
     const navbarToggle = document.querySelector('.navbar__toggle');
     const navbarLinks = document.querySelector(".navbar__links");
     const navbarLinkItems = document.querySelectorAll(".navbar__links li a");