Update minimum Node versions in docs

[JESii]

Closes #7181

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[JESii]

Can't imagine why some of the checks failed -- I made a one-line change on README.md :=)

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[JESii]

All checks have passed, and there are no conflicts. Should be able to be merged... yes?

[iansu]

Thanks!