Added section about passing options to request

[stylesuxx]

When you want to pass options to the request call, it is not enough to set them in the options argument, they need to be within the key requestOptions.

Also I think, that the user passed options should be the last ones applied and override anything that is set by the library. Right now the library is overwriting some of the options.

I would suggest setting the user options for requests before the actual call to request:

https://github.com/chill117/proxy-verifier/blob/ff1d21e9d3c429de2ead426848b061ed1a82579f/index.js#L388

I am aware this can break the call - but if the user is passing options to request, I guess he knows what he is doing.

If you like the idea I can submit a PR.