Modify readme

Add clarification.

README.md

@@ -70,7 +70,7 @@ export const getServerSideProps = Iceform.action.getServerSideProps(greet);
 ```
 
 Lastly, define the form page:
-```tsx
+```ts
 // [src/]pages/form.tsx
 
 import * as React from 'react';
@@ -85,6 +85,7 @@ const FormPage: Iceform.NextPage = ({
 
 	const [responseData, setResponseData] = React.useState<unknown>();
 	React.useEffect(() => {
+		// response.bodyUsed might be undefined, so we use a strict comparison
 		if (response?.bodyUsed === false) {
 			response?.json().then((responseData) => {
 				setResponseData(responseData);

packages/iceform-next-sandbox/src/pages/greet.tsx

@@ -9,6 +9,7 @@ const GreetPage: Iceform.NextPage = ({
 
   const [responseData, setResponseData] = React.useState<unknown>();
   React.useEffect(() => {
+		// response.bodyUsed might be undefined, so we use a strict comparison
 		if (response?.bodyUsed === false) {
 			response?.json().then((responseData) => {
 				setResponseData(responseData);