docs: add vulnerability disclosure policy

Kyle Teerequested to merge
LordParsley/exosphere:chore/vulnerability-disclosures into master

Overview

Resolves #1086 (closed) by adding a vulnerability disclosure policy.

(With some safe harbour inspiration from https://docs.hackerone.com/en/articles/8494502-safe-harbor-overview-faq.)

How to Test

Review the new policy on this branch.

Merge request reports