chore: add CONTRIBUTING.md

Author: m0n0x41d

CONTRIBUTING.md

@@ -0,0 +1,26 @@
+# Contributing to Quint Code
+
+## Workflow
+
+1. **Create an issue first** — Open an issue with the `proposal` label. Include:
+   - Rationale — either FPF methodology alignment or UX improvement (feature request)
+   - Question or problem statement
+   - Proposed solution
+
+2. **Wait for agreement** — Do not create a PR until the proposal has been discussed and agreed upon in the issue.
+
+3. **Check for existing work** — Before starting, verify no one else has picked up the same issue. Comment on the issue to claim it.
+
+4. **Create PR to `dev` branch** — When ready, open a pull request targeting `dev`, not `main`. Link the original issue.
+
+5. **Update the changelog** — Add your changes to `CHANGELOG.md` under the `[Unreleased]` section.
+
+## Want to Help but No Proposal?
+
+Check existing issues labeled `bug`, `documentation`, or `help wanted`. Leave a comment to express interest and wait for approval before starting work.
+
+## Summary
+
+```
+Issue (proposal label) → Agreement → Claim issue → PR to dev → Update changelog
+```

README.md

@@ -99,6 +99,7 @@ See [docs/fpf-engine.md](docs/fpf-engine.md) for the full breakdown.
 
 - [FPF Engine Details](docs/fpf-engine.md) — ADI cycle, commands, when to use
 - [Architecture](docs/architecture.md) — Internals, knowledge levels, Transformer Mandate
+- [Contributing](CONTRIBUTING.md) — How to contribute
 
 ## License