Please do not encourage monkey-patching global fetch

[uvdsl]

I thought I would raise a voice for not encouraging monkey-patching and especially not encouraging monkey-patching global fetch as the current readme does.

Just to reference some previous discussion that might be helpful to you:

• What is the reason to patch the fetch? react/react#25573
• https://www.reddit.com/r/javascript/comments/1cmhfyy/why_patching_globals_is_harmful/

Thank you.

[uvdsl]

Noting that both #21 and #22 try to fix symptoms of patching global fetch.