feat(docs): button to switch dark and light mode (nodejs#4044)

Author: shivarm

docs/index.html

@@ -8,6 +8,12 @@
   <meta name="description" content="A HTTP/1.1 client, written from scratch for Node.js.">
   <meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1.0">
   <link rel="stylesheet" href="//cdn.jsdelivr.net/npm/docsify@4/lib/themes/vue.css">
+  <link
+  rel="stylesheet"
+  href="//cdn.jsdelivr.net/npm/docsify-darklight-theme@latest/dist/style.min.css"
+  title="docsify-darklight-theme"
+  type="text/css"
+/>
   <link rel="icon" type="image/png" href="https://nodejs.org/static/images/favicons/favicon.png" />
 </head>
 
@@ -81,6 +87,10 @@
   <script src="//cdn.jsdelivr.net/npm/docsify@4"></script>
   <script src="//cdn.jsdelivr.net/npm/docsify/lib/plugins/search.min.js"></script>
   <script src="https://unpkg.com/docsify-copy-code@3"></script>
+  <script
+  src="//cdn.jsdelivr.net/npm/docsify-darklight-theme@latest/dist/index.min.js"
+  type="text/javascript"
+></script>
   <script type="module">
     import mermaid from "//cdn.jsdelivr.net/npm/[email protected]/+esm";
     mermaid.initialize({ startOnLoad: true });