docs: add description for `outputs.pr` (#520)
docs: add description for `outputs.pr` (#520)

* docs: fix description of `outputs.pr`

* docs: add `outputs.prs` to README.md

Co-authored-by: Jeff Ching <21aaffda9718a203d3f6dfde95bf7c5668b929a6@google.com>
google-github-actions/release-please-action