ci(release.sh): add link to changelog to release body

[skyfrk]

Adds a link to https://github.com/phrase/openapi/blob/master/clients/cli/CHANGELOG.md to the body of the release, so that the changelog can easily be found by users that are subscribed to new releases.

[skyfrk]

Docs: https://docs.github.com/en/rest/releases/releases?apiVersion=2022-11-28#create-a-release