Update file tree in README to point out pybind11

[azeey]

🦟 Bug fix

Summary

A small update to point out we use pybind11 for Python instead of SWIG

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• 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 and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #558 (98ea093) into gz-math7 (bba92d7) will not change coverage.
The diff coverage is n/a.

❗ Current head 98ea093 differs from pull request most recent head 14064b8. Consider uploading reports for the commit 14064b8 to get more accurate results

@@            Coverage Diff            @@
##           gz-math7     #558   +/-   ##
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  Coverage     94.16%   94.16%           
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  Files           145      145           
  Lines          9774     9774           
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  Hits           9204     9204           
  Misses          570      570