docs: add README with install and usage instructions

README.md

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+# circuitforge-hooks
+
+Centralised git hooks for all CircuitForge repos.
+
+## What it does
+
+- **pre-commit** — scans staged changes for secrets and PII via gitleaks
+- **commit-msg** — enforces conventional commit format
+- **pre-push** — scans full branch history as a safety net before push
+
+## Install
+
+From any CircuitForge product repo root:
+
+```bash
+bash /Library/Development/CircuitForge/circuitforge-hooks/install.sh
+```
+
+On Heimdall live deploys (`/devl/<repo>/`), add the same line to the deploy script.
+
+## Per-repo allowlists
+
+Create `.gitleaks.toml` at the repo root to extend the base config:
+
+```toml
+[extend]
+path = "/Library/Development/CircuitForge/circuitforge-hooks/gitleaks.toml"
+
+[allowlist]
+regexes = [
+    '\d{10}\.html',   # example: Craigslist listing IDs
+]
+```
+
+## Testing
+
+```bash
+bash tests/test_hooks.sh
+```
+
+## Requirements
+
+- `gitleaks` binary: `sudo apt-get install gitleaks`
+- bash 4+
+
+## Adding a new rule
+
+Edit `gitleaks.toml`. Follow the pattern of the existing `[[rules]]` blocks.
+Add tests to `tests/test_hooks.sh` covering both the blocked and allowed cases.