update doc

docs/advanced-features/dynamic-import.md

@@ -180,5 +180,21 @@ function Home() {
 export default Home
 ```
 
-If you set option `suspense` to true, both option `ssr` and `loading` will be omitted, delegating rendering control to React `<Suspense />`.
+If you set option `suspense` to true, other options will be omitted, delegating rendering control to React `<Suspense />`.
 It's similar to using `React.lazy` directly, but `next/dynamic` will support mode like CSR and SSG.
+
+To use `suspense`, you need to enable `reactRoot` and `concurrentFeatures` in `next.config.js`.
+
+Note: `reactRoot` will be enabled by default when using React 18.
+
+```jsx
+// next.config.js
+module.exports = {
+  experimental: {
+    reactRoot: true,
+    concurrentFeatures: true,
+  },
+}
+```
+
+If you only enable `reactRoot` but not `concurrentFeatures`, suspense will always render fallbacks on server side.