Revise merge request approvals rule page, CTRT
Revises the newly-created user/project/merge_requests/approvals/rules.md
(split apart from https://docs.gitlab.com/ee/user/project/merge_requests/approvals/index.html in #324948 (closed)) to bring it up to CTRT standards. Also tone and style polish, header renaming, etc.
Related issues
- Related to #324948 (closed) where the need was identified.
Edited by Amy Qualls