Add note about optix in README

[iche033]

🦟 Bug fix

Summary

Tweak to README about optix. Marked it as experimental since it's not very well maintained.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge

[codecov]

Codecov Report

Merging #425 (6e89b2d) into main (35087de) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #425   +/-   ##
=======================================
  Coverage   55.11%   55.11%           
=======================================
  Files         192      192           
  Lines       19383    19383           
=======================================
  Hits        10682    10682           
  Misses       8701     8701           

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