docs: improve explanation about body option (#276)

* docs: improve explanation about `body` option

* add note about buffer too + improves

* update

---------

Co-authored-by: Pooya Parsa <pooya@pi0.io>

README.md

@@ -67,7 +67,15 @@ await ofetch("/api/generate-image", { responseType: "blob" });
 
 ## ✔️ JSON Body
 
-`ofetch` automatically stringifies request body (if an object is passed) and adds JSON `Content-Type` and `Accept` headers (for `put`, `patch` and `post` requests).
+If an object or a class with a `.toJSON()` method is passed to the `body` option, `ofetch` automatically stringifies it.
+
+`ofetch` utilizes `JSON.stringify()` to convert the passed object. Classes without a `.toJSON()` method have to be converted into a string value in advance before being passed to the `body` option.
+
+For `PUT`, `PATCH`, and `POST` request methods, when a string or object body is set, `ofetch` adds the default `content-type: "application/json"` and `accept: "application/json"` headers (which you can always override).
+
+Additionally, `ofetch` supports binary responses with `Buffer`, `ReadableStream`, `Stream`, and [compatible body types](https://developer.mozilla.org/en-US/docs/Web/API/fetch#body). ofetch will automatically set the `duplex: "half"` option for streaming support!
+
+**Example:**
 
 ```js
 const { users } = await ofetch("/api/users", {