Create a Security Policy

Hi, I've noticed that the security policy got lost in this recent changing in the repo. I believe it was using the github standard security policy before https://github.com/github/.github/blob/main/SECURITY.md.

Since this is an important document to ensure a safe and timely vulnerability report process, I'd like to suggest to define one for jakechampion/fetch repository.

There are a few ways to receive such disclosures:

have an email or website available to receive such reports (such as opensource-security[@]github.com); and/or
use GitHub's private vulnerability reporting feature.

Let me know if a PR suggesting a Security Policy is welcome and I'll submit it ASAP.

JakeChampion / fetch

Create a Security Policy #1373