Add CONTRIBUTING.md with scoped contribution paths

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Cüneyt Öztürk

CONTRIBUTING.md

@@ -0,0 +1,29 @@
+# Contributing
+
+PRML and its reference implementations are open standards work. Issues, PRs, and design pushback are welcome.
+
+## Quick paths
+
+- **Found a bug:** open an issue with a minimal repro.
+- **Spec-level question:** ask in [studio-11-co/falsify-hackathon discussions](https://github.com/studio-11-co/falsify-hackathon/discussions). Repo-level questions stay here.
+- **Want to add code:** see `good-first-issue` and `help-wanted` labels for scoped work. For larger changes open an issue first so we can align on shape before you write a long PR.
+
+## Pull requests
+
+- Keep PRs small and focused. One change per PR.
+- Reference the issue number in the PR body if one exists.
+- Tests: add or update where relevant. CI must be green before review.
+- Commit messages: imperative mood, one short summary line, optional body. No emoji.
+- v0.1 conformance: any change that alters canonical-byte output must preserve byte-equivalence across the 20 conformance vectors. CI catches this.
+
+## Code of conduct
+
+Be direct, be technical, no harassment. Decisions on what gets merged are the maintainer's call.
+
+## License
+
+By contributing you agree that your work is released under the repo's stated license (see `LICENSE`).
+
+## Maintainer
+
+Cüneyt Öztürk — hello@studio-11.co