[DOC] remove warning from experimental module and add it as doc string

[Remi-Gau]

• Relates to [ENH] Next steps for development on experimental surface module #4027 (comment)

Changes proposed in this pull request:

• remove warning from experimental module
• add it as part of the doc string to be rendered in the doc

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d0cbdcd) 92.06% compared to head (495f19b) 92.06%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4240      +/-   ##
==========================================
- Coverage   92.06%   92.06%   -0.01%     
==========================================
  Files         144      144              
  Lines       16421    16419       -2     
  Branches     3434     3434              
==========================================
- Hits        15118    15116       -2     
  Misses        761      761              
  Partials      542      542              

Flag	Coverage Δ
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macos-latest_3.9_test_plotting	?
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windows-latest_3.9_test_plotting	91.79% <ø> (-0.01%)	⬇️

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[bthirion]

Good with me.

[jeromedockes]

LGTM, thanks!