docs: add local development guide

docs/local-dev.md

@@ -0,0 +1,62 @@
+# Local development
+
+## Prerequisites
+
+- Git
+- Rust toolchain (stable): `rustup` + `cargo`
+- C/C++ build tools in `PATH` (required by Rust dependencies)
+
+Quick check:
+
+```bash
+git --version
+rustc --version
+cargo --version
+```
+
+## Setup
+
+```bash
+git clone https://github.com/malon64/floe.git
+cd floe
+
+# Optional: ensure stable toolchain is available
+rustup default stable
+
+# Pre-fetch dependencies for faster first build/test
+cargo fetch
+```
+
+## Run
+
+Use the example contract in this repo:
+
+```bash
+cargo run -p floe-cli -- validate -c example/config.yml
+cargo run -p floe-cli -- run -c example/config.yml
+```
+
+## Test
+
+Run the main crate tests:
+
+```bash
+cargo test -p floe-core
+cargo test -p floe-cli
+```
+
+## Quality checks
+
+Run formatting and lint checks before opening a PR:
+
+```bash
+cargo fmt --all
+cargo clippy --all-targets --all-features -- -D warnings
+```
+
+## Troubleshooting
+
+- `cargo` command not found: install Rust with `rustup`, then restart your shell.
+- Build fails on native deps: install your OS C/C++ toolchain, then rerun `cargo build`.
+- `example/config.yml` not found: run commands from the repository root (`floe/`).
+- CLI command succeeds but output is unexpected: run `floe validate` first to catch contract issues early.