fix: fetch body is not Readable

It's much easier to implement spec compliant fetch API if
we don't try to be node streams at the same time.

Author: ronag

README.md

@@ -161,6 +161,8 @@ https://fetch.spec.whatwg.org/
 
 Implements [fetch](https://fetch.spec.whatwg.org/).
 
+Only supported on Node 16+.
+
 This is [experimental](https://nodejs.org/api/documentation.html#documentation_stability_index) and is not yet fully compliant the Fetch Standard. We plan to ship breaking changes to this feature until it is out of experimental.
 
 Arguments:

docs/api/Dispatcher.md

@@ -307,36 +307,11 @@ client.dispatch({
 
 ### `Dispatcher.fetch(options)`
 
-Performs a HTTP request.
-
 Implements [fetch](https://fetch.spec.whatwg.org/).
 
-This is [experimental](https://nodejs.org/api/documentation.html#documentation_stability_index) and is not yet fully compliant the Fetch Standard. We plan to ship breaking changes to this feature until it is out of experimental.
-
-Arguments:
-
-* **options** `FetchOptions`
-
-Returns: `Promise<FetchResponse>`
+Only supported on Node 16+.
 
-#### Parameter: `FetchOptions`
-
-Extends: [`DispatchOptions`](#parameter-dispatchoptions)
-
-**headers** `HeadersInit`
-**body** `BodyInit?`
-**keepalive** `boolean`
-**signal** `AbortSignal?`
-
-#### Parameter: `FetchResponse`
-
-* **type** `ResponseType`
-* **url** `string`
-* **redirected** `boolean`
-* **status** `number`
-* **ok** `boolean`
-* **statusText** `string` Always empty string.
-* **headers** `Headers`
+This is [experimental](https://nodejs.org/api/documentation.html#documentation_stability_index) and is not yet fully compliant the Fetch Standard. We plan to ship breaking changes to this feature until it is out of experimental.
 
 ### `Dispatcher.pipeline(options, handler)`