docs: add details to redirects file (#15020)

website/redirects.js

+/**
+ * Define your custom redirects within this file.
+ *
+ * Vercel's redirect documentation:
+ * https://nextjs.org/docs/api-reference/next.config.js/redirects
+ *
+ * Relative paths with fragments (#) are not supported.
+ * For destinations with fragments, use an absolute URL.
+ *
+ * Playground for testing url pattern matching: https://npm.runkit.com/path-to-regexp
+ *
+ * Note that redirects defined in a product's redirects file are applied to
+ * the developer.hashicorp.com domain, which is where the documentation content
+ * is rendered. Redirect sources should be prefixed with the product slug
+ * to ensure they are scoped to the product's section. Any redirects that are
+ * not prefixed with a product slug will be ignored.
+ */
 module.exports = [
+  /*
+  Example redirect:
+  {
+    source: '/nomad/docs/internal-docs/my-page',
+    destination: '/nomad/docs/internals/my-page',
+    permanent: true,
+  },
+  */
   // Rename and re-arrange Autoscaling Internals section
   {
     source: '/nomad/tools/autoscaling/internals/:path*',