x/vuln: add privacy policy to README
x/vuln: add privacy policy to README

Change-Id: I284e8accd60c63f156b68ffdafbd0f9bbcb61fc5
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/421422
Reviewed-by: Julie Qiu <e6cb64861edcc38971590ff27c111e0e672de045@google.com>

golang/vuln,golang/vuln