Add contributing guide

CONTRIBUTING.md

@@ -0,0 +1,37 @@
+# Contributing to Lambda CLI
+
+## Development
+
+```bash
+git clone https://github.com/Strand-AI/lambda-cli.git
+cd lambda-cli
+cargo build
+cargo test
+```
+
+## Pull Requests
+
+1. Fork the repo and create a branch
+2. Make your changes
+3. Run `cargo fmt` and `cargo clippy`
+4. Open a PR against `main`
+
+## Releasing
+
+Releases are automated via PR labels. To create a release:
+
+1. Open a PR with your changes
+2. Add one of these labels:
+   - `release:patch` - Bug fixes (0.2.0 → 0.2.1)
+   - `release:minor` - New features (0.2.0 → 0.3.0)
+   - `release:major` - Breaking changes (0.2.0 → 1.0.0)
+3. Merge the PR
+
+When merged, CI will automatically:
+- Bump the version in `Cargo.toml`
+- Create a git tag
+- Build binaries for Linux and macOS
+- Create a GitHub release
+- Update the Homebrew formula
+
+No label = no release. PRs without release labels are regular code changes.