docs: mdx, light/dark mode, ask (#400)

docs/next.config.mjs

@@ -0,0 +1,10 @@
+import createMDX from "@next/mdx";
+
+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  pageExtensions: ["js", "jsx", "ts", "tsx", "md", "mdx"],
+};
+
+const withMDX = createMDX({});
+
+export default withMDX(nextConfig);