Fix template links for links to PRs

[joestringer]

The templates for a PR to add yourself to the org refers to URLs that have @me in them. Unfortunately this means that when the contributor proposes their PR and clicks on the link it works for them... but when reviewers click the link it shows the reviewer's PRs, not the contributor's PRs.

We should change the template to instead have some text like REPLACE-ME to indicate to the contributor that they need to modify the URL before posting the PR.