Add note about empty request body

[mifi]

Checklist

• I have read the documentation.
• I have included a pull request description of my changes.
• I have included some tests.
• If it's a new feature, I have included documentation updates in both the README and the types.

I literally spent hours trying to figure out why my requests were hanging, when sending a POST, but not when sending a GET. And only when using isStream: true, not with isStream: false

[sindresorhus]

We should either just gracefully handle this or throw an error.

[szmarczak]

The note is already here.

[mifi]

Thanks! I missed that. Maybe I can add an example for the no-body use case too?

[szmarczak]

Buffer.alloc(0) is quite useless when you can just pass an empty string.

Feel free to move the note above if it's more noticeable.

[mifi]

I updated the PR. An alternative solution to avoid issues like this could be to have one isStream option for the request and one for the response, maybe isRequestStream and isResponseStream.