Clarify cURL dependency

here it says cURL is a dependency:

https://github.com/spotify/NFHTTP#dependencies-globe_with_meridians

but here it says cURL is not used with Windows:

https://github.com/spotify/NFHTTP#architecture-triangular_ruler

so is cURL actually needed when compiling for Windows?

[drubinstein]

I'll update the readme. Windows uses WinHTTP as you read in the README so curl isn't needed.