[AI] docs: note aws-lc and s2n-tls are required on macOS

[sfod]

Note: This PR was generated by an AI assistant on behalf of the author.

Summary

Update README to reflect that aws-lc and s2n-tls are required on macOS in
addition to Linux. Previously the section was titled "Linux-Only Dependencies"
and only mentioned Linux.

Changes

• Rename "Linux-Only Dependencies" section to "Linux and macOS Dependencies"
• Update the sentence to say "Linux or macOS" instead of just "Linux"

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.61%. Comparing base (2ef9605) to head (9fa97cc).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #428      +/-   ##
==========================================
- Coverage   84.65%   84.61%   -0.05%     
==========================================
  Files          26       26              
  Lines       11088    11088              
==========================================
- Hits         9387     9382       -5     
- Misses       1701     1706       +5     

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