make link from the PR template absolute to website checklist

Author: nsryan2

.github/pull_request_template.md

@@ -30,5 +30,5 @@
 
 ## Checklist for Reviewers
 
-Reviewers should use [this link](/manual/guides/pull_requests.md) to get to the 
+Reviewers should use [this link](https://arfc.github.io/manual/guides/pull_requests) to get to the
 Review Checklist before they begin their review.