docs: explain how to include predefined globals

[mlwyatt]

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What is the purpose of this pull request? (put an "X" next to an item)

[X] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
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[ ] Other, please explain:

What changes did you make? (Give an overview)

I've added a note about how to enable native globals as discussed in #17101 (reply in thread)

Is there anything you'd like reviewers to focus on?

I think the wording is pretty clear, but let me know if not.

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• ✅ login: mlwyatt / name: Marcus Wyatt (0ddcfca, 0af67d3)

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[amareshsm]

LGTM. Leaving it open for others to verify once.

[mdjermanovic]

LGTM, thanks! Leaving it open for @fasttime to verify.

[fasttime]

Thanks @mlwyatt! I've changed "native globals" to "predefined globals" in the title because some environments define globals that are not native (e.g. mocha's describe, it, etc.).

[fasttime]

LGTM

[mdjermanovic]

@mlwyatt could you please submit the same changes again, in a new PR, as we had to undo them due to #17225.