[Sim, UX] Add multisim instrs to predictoor.md

[trentmc]

Background / motivation

In #779, we added a new multisim command for easier benchmarking in sims.

• PR #783
• Commit e9795f5

Instructions on how to use were added to the CLI, good.

But there's another place to link to it: the "optimize model" section of predictoor.md. And, perhaps add 2-4 lines about hinting how to use it.

That's the aim of this issue.

TODOs / DoD

Add 2-4 lines in "optimize model" section as discussed above.