Enh: make it easier for editors to find the reviewer "database" / spreadsheet

[lwasser]

We have a reviewer signup document that is read only with only names and github usernames for reviewers that we use to contact reviewers. Add a link to that document in our peer review guide within the editor guide page.

I suggest that we add language here that says

pyOpenSci maintains a list of people who have volunteered to review for pyOpenSci. Use this resource to help you find reviewers and be sure to leave a comment if you reach out to someone so multiple editors don't reach out to the same person around the same time!

@sneakers-the-rat from a privacy standpoint - that spreadsheet doesn't have any demographic info but it DOES have people's emails. i'm curious what you think about that and if there is some way to allow people access to that data without allowing the world access to people's emails.