docs: incorporate some AI guidance for contributors

[rtyler]

This what @thisisnic suggested via apache/arrow#48952 and has discussed
on the Apache Arrow developers mailing list. I think this is good
guidance to start with for AI contributions

Signed-off-by: R. Tyler Croy rtyler@brokenco.de

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.05%. Comparing base (987e535) to head (76c489b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4131      +/-   ##
==========================================
- Coverage   76.07%   76.05%   -0.02%     
==========================================
  Files         164      164              
  Lines       44846    44824      -22     
  Branches    44846    44824      -22     
==========================================
- Hits        34115    34092      -23     
- Misses       9111     9113       +2     
+ Partials     1620     1619       -1     

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