Explain more about what to and what not to review for JiHu

Why is this change being made?

Explain more about what to and what not to review for JiHu

It's not exactly clear what and why changes should go anywhere, this should expand on that.

Internal Slack context: https://gitlab.slack.com/archives/C01S3DV4MSR/p1636630148037300

I did not clearly understand we were accepting only DB changes. I could not see a reference to this here.

Review app: https://what-to-review-jh.about.gitlab-review.app/handbook/ceo/chief-of-staff-team/jihu-support/jihu-contribution-review-process.html

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this change to the correct DRI(s)
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• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR.
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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