Create CONTRIBUTING.md

Author: tidwall

CONTRIBUTING.md

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+# Contributing
+
+Thanks for your interest in improving Tile38!
+
+## Issues
+- **Found a bug?** Please open an issue with a clear description and precise steps to reproduce.
+
+## Pull Requests
+- **Scope.** PRs are welcome for bug fixes and small, low-risk changes.
+- **Please coordinate first.** For large changes, such as new features, please file an issue and/or discuss it with a maintainer beforehand.
+- **Quality.** Keep PRs focused, include tests (where applicable), and update docs.
+
+## When Not to use a Pull Request
+
+Do NOT submit a Pull Request for:
+
+- Security-related changes.
+- Works in progress.
+- Changes that require design discussion, or are likely to be controversial.
+- Changes needing specialized or cross-subsystem review.
+- Large refactors or mechanical tree-wide changes.
+- Changes generated by AI tools.
+
+## AI Assisted Contributions
+
+We are not accepting AI assisted code into Tile38 at this time. 
+This policy may change in the future. 
+Please reach out if you have any questions or concerns regarding AI and Tile38.
+
+### Contributor Responsibilities
+
+- Monitor your Pull Request and respond to review feedback promptly.
+- Pull Requests may be closed if there is no response for **one month**.
+
+By submitting a contribution, you confirm you have the right to do so and grant Tile38 LLC the rights needed to use, modify, and redistribute your contribution as part of the project.
+
+If you have any questions or concerns regarding licensing, please contact us at licensing@tile38.com.  
+For all other questions, contributing@tile38.com.