docs: add bundle redirect page

pages/css/bundle.js

@@ -0,0 +1,18 @@
+import {rootPage} from '../../docs/utils'
+
+export default class {
+  static getInitialProps({query: {name}, res}) {
+    const url = getBundleURL(name)
+    if (url) {
+      res.writeHead(303, {Location: url})
+    } else {
+      res.writeHead(404)
+    }
+    res.end()
+  }
+}
+
+function getBundleURL(bundle) {
+  const node = rootPage.first(node => node.meta.bundle === bundle)
+  return node ? node.path : `/_error`
+}