add missing await to setupDevPlatform call in next-dev readme (#668)

internal-packages/next-dev/README.md

@@ -53,8 +53,10 @@ export default nextConfig;
 // we only need to use the utility during development so we can check NODE_ENV
 // (note: this check is recommended but completely optional)
 if (process.env.NODE_ENV === 'development') {
-	// we simply need to call the utility
-	setupDevPlatform();
+	// `await`ing the call is not necessary but it helps making sure that the setup has succeeded.
+	//  If you cannot use top level awaits you could use the following to avoid an unhandled rejection:
+	//  `setupDevPlatform().catch(e => console.error(e));`
+	await setupDevPlatform();
 }
 ```