Add docs section on explicitness when assigning reviewers

What does this MR do and why?

• This is a practice that I have adopted by observing others do it.
• As an MR reviewer, I find that this saves me time because it removes any ambiguity about the type of review that is being sought from me.
• I also enjoy the human element of this. It adds some noise but feels more friendly than being silently assigned to review something.
• Example: !109734 (comment 1251245803)

Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.