Inform OpenJS Maintainers of new CNA

[ruddermann]

Before going live with the CNA we should let project maintainers know what we're doing, how this impacts them, and how they can engage with the CNA.

To this end I've written a CNA Guide for Maintainers gDoc here: https://docs.google.com/document/d/1AID4IacA-58UzJYe2FC76knEuABWZ37L-a4KiYJ_bm4/edit?tab=t.7o5bs9f5vuq7

Initially we will send the gDoc to maintainers. After the doc is tested IRL, we'll update it and move it to GitHub.