Add a CLAUDE.md file

Author: mairas

CLAUDE.md

@@ -0,0 +1,48 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This repository contains the HALPI2 User Guide documentation, built with mdBook. HALPI2 is a Raspberry Pi Compute Module 5 carrier board designed for marine electronics and industrial applications.
+
+## Build System
+
+**Prerequisites:** Rust and Cargo must be installed. Then install mdBook:
+```bash
+cargo install mdbook
+```
+
+**Common Commands:**
+- `mdbook build` - Build the documentation (output goes to `./book`)
+- `mdbook serve --open` - Start local dev server and open in browser
+- `mdbook test` - Test code samples in the documentation
+- `mdbook clean` - Remove the build directory
+
+## Documentation Structure
+
+- `src/SUMMARY.md` - Table of contents (mdBook navigation structure)
+- `src/` - All markdown content organized by section:
+  - `getting-started/` - Quick start and installation guides
+  - `user-guide/` - System operation, hardware, interfaces, software
+  - `technical-reference/` - Detailed hardware specs and technical docs
+  - `software-development/` - Daemon, integration, Ubuntu installation
+  - `appendices/` - Design files, schematics, errata
+- `theme/` - Custom CSS/JS for page TOC functionality
+- `book.toml` - mdBook configuration
+
+## Documentation Status
+
+Check `src/SUMMARY.md` for completion status of each page (✅ = complete, ❌ = incomplete/placeholder).
+
+## Deployment
+
+GitHub Actions automatically builds and deploys to GitHub Pages on push to `main` branch. See `.github/workflows/mdbook.yml`.
+
+## Content Guidelines
+
+- Use GitHub-flavored Markdown
+- Include images with descriptive alt text
+- Cross-reference other pages using relative paths
+- Technical specs and measurements should be in the technical-reference section
+- Step-by-step instructions belong in getting-started or user-guide sections