Add example for request + "Garbage Collection" (#3916)

* Add example for `request` + "Garbage Collection"

* `dump` never throws without a signal

* fix code (response !== res)

* async await

* add "force consumption of body" comment

README.md

@@ -281,17 +281,23 @@ stalls or deadlocks when running out of connections.
 
 ```js
 // Do
-const headers = await fetch(url)
-  .then(async res => {
-    for await (const chunk of res.body) {
-      // force consumption of body
-    }
-    return res.headers
-  })
+const { body, headers } = await fetch(url);
+for await (const chunk of body) {
+  // force consumption of body
+}
 
 // Do not
-const headers = await fetch(url)
-  .then(res => res.headers)
+const { headers } = await fetch(url);
+```
+
+The same applies for `request` too:
+```js
+// Do
+const { body, headers } = await request(url);
+await res.body.dump(); // force consumption of body
+
+// Do not
+const { headers } = await request(url);
 ```
 
 However, if you want to get only headers, it might be better to use `HEAD` request method. Usage of this method will obviate the need for consumption or cancelling of the response body. See [MDN - HTTP - HTTP request methods - HEAD](https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/HEAD) for more details.