Clarify in docs when ViewCoordinate is picked up by a 3D view

[Wumpf]

What

• Fixes ViewCoordinates documentation is wrong or at least misleading #7028

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!
• If have noted any breaking changes to the log API in CHANGELOG.md and the migration guide

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Deployed docs

Commit	Link
9a863b3	https://landing-44u6e1x8g-rerun.vercel.app/docs