Better document limited effect of DepthMeter & FillRatio in 2D views

[Wumpf]

What

• Part of Not all items in override UI always apply to visualizers #6595

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
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• 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
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Deployed docs

Commit	Link
8df291c	https://landing-k251wp3ij-rerun.vercel.app/docs