Document differences between Node.js fetch() implementations and the standard

[mcollina]

We should add a section in our docs documenting how/why Node.js fetch() differs from the standard.

A few notable differences

• new Response(asyncIterable) is an addition to standard
• cookies handling
• no forbidden headers

@KhafraDev definitely know more

[KhafraDev]

Most of these are documented in undici's README, it should be pretty easy to copy the documentation from there. https://github.com/nodejs/undici?tab=readme-ov-file#undicifetchinput-init-promise

[AretiTsolakidou]

I totally agree, giving users the opportunity to know what Node.js fetch() is in both the documentation and in README will turn out to be very helpful.