chore(docs): improve docs for withResponse/asResponse

Author: stainless-ci-bot

README.md

@@ -367,8 +367,10 @@ const message = await client.messages.create(
 ### Accessing raw Response data (e.g., headers)
 
 The "raw" `Response` returned by `fetch()` can be accessed through the `.asResponse()` method on the `APIPromise` type that all methods return.
+This method returns as soon as the headers for a successful response are received and does not consume the response body, so you are free to write custom parsing or streaming logic.
 
 You can also use the `.withResponse()` method to get the raw `Response` along with the parsed data.
+Unlike `.asResponse()` this method consumes the body, returning once it is parsed.
 
 <!-- prettier-ignore -->
 ```ts