docs: add note about experimental features

[jooola]

• Document how users can learn about experimental features.
• Document how developers can release experimental features.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.43%. Comparing base (d62bb5f) to head (ecfda0e).
⚠️ Report is 44 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #520   +/-   ##
=======================================
  Coverage   93.43%   93.43%           
=======================================
  Files          64       64           
  Lines        3048     3048           
=======================================
  Hits         2848     2848           
  Misses        200      200           

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