Update Merge request diffs storage page based on initial review

Issue description

This page describes product documentation work that was identified during a documentation review of documentation pages associated with the Create:Editor stage/group.

Page: https://docs.gitlab.com/ee/administration/merge_request_diffs.html

Identified items

• This page feels marooned. I suspect grepping for merge request diff will turn up some places we should cross-link it.
• Move ... if your terminal does not support ANSI escape codes to the ANSI variable it references.