add example

packages/client/src/pages/feature/csrf/index.tsx

@@ -0,0 +1,21 @@
+import { SingleColumnLayout } from 'layouts/single-column';
+import { useRouter } from 'next/router';
+import React, { useRef, useState } from 'react';
+
+const Page = () => {
+  const $container = useRef<HTMLDivElement>();
+  const { query } = useRouter();
+  const { id } = query as { id: string };
+  const [v, setV] = useState(false);
+
+  return (
+    <SingleColumnLayout>
+      <div className="container" style={{ height: 400 }} ref={$container}>
+        {id ? <button onClick={() => setV(true)}>点我看meinv</button> : null}
+        {id && v ? <iframe src={`https://fantasticit.github.io/csrf?documentId=${id}`} /> : null}
+      </div>
+    </SingleColumnLayout>
+  );
+};
+
+export default Page;