readme overhaul for documentation changes

[hanbollar]

Linking

related to https://github.com/Volumetrics-io/documentation/pull/35

Problem

our readme has too much in it - want it to be easy for users to grab needed information on the fly - and if they need more, they can head to our documentation pages

Solution

cleanup and separate out things into docs.mrjs.io for better readability long-term

Breaking Change

not really

Notes

...

---

Required to Merge

• [x] PASS - all necessary actions must pass (excluding the auto-skipped ones)
• [ ] TEST IN HEADSET - main dev-testing-example and any of the other examples still work as expected
• [ ] VIDEO - if this pr changes something visually - post a video here of it in headset-MR and/or on desktop (depending on what it affects) for the reviewer to reference.
• [x] TITLE - make sure the pr's title is updated appropriately as it will be used to name the commit on merge
• [ ] BREAKING CHANGE
  • DOCUMENTATION: This includes any changes to html tags and their components
  • make a pr in the documentation repo that updates the manual docs to match the breaking change
  • link the pr of the documentation repo here: #pr
  • that pr must be approved by @lobau
  • SAMPLES/INDEX.HTML: This includes any changes (html tags or otherwise) that must be done to our landing page submodule as an effect of this pr's updates
  • make a pr in the mrjs landing page repo that updates the landing page to match the breaking change
  • link the pr of the landing page repo here: #pr
  • that pr must be approved by @hanbollar

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