add copilot-instructions.md

Signed-off-by: Tuomo Tanskanen <[email protected]>

Author: tuminoid

.github/copilot-instructions.md

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+# Metal3 Documentation - AI Coding Assistant Instructions
+
+## Project Overview
+
+Central documentation repository for the Metal3 project using Hugo
+static site generator. Contains architecture docs, user guides, API
+references, and deployment workflows. Published at
+<https://book.metal3.io>
+
+## Structure
+
+- `docs/` - Main documentation content (Markdown)
+   - `user-guide/` - End-user documentation
+   - `dev-env/` - Development environment setup
+   - `api/` - API references
+   - `architecture/` - Design documents
+- `themes/` - Hugo theme customization
+- `config.toml` - Hugo configuration
+- `Makefile` - Build and serve commands
+
+## Local Development
+
+```bash
+# Install Hugo
+# Ubuntu: sudo snap install hugo
+# macOS: brew install hugo
+
+# Serve docs locally with live reload
+make serve
+
+# Build static site
+make build
+
+# Output in docs/_site/
+```
+
+## Adding Documentation
+
+1. Create new Markdown file in appropriate `docs/` subdirectory
+
+2. Add frontmatter:
+
+   ```yaml
+   ---
+   title: "Your Page Title"
+   weight: 10  # Ordering in navigation
+   ---
+   ```
+
+3. Write content in Markdown
+
+4. Test locally with `make serve`
+
+5. Submit PR
+
+## Documentation Guidelines
+
+- Use clear, concise language
+- Include code examples for technical content
+- Add diagrams for architecture/workflows (use mermaid or images)
+- Cross-link related pages
+- Keep API docs in sync with actual APIs
+- Test all commands/examples before publishing
+
+## Common Pitfalls
+
+1. **Broken Links** - Check internal links before committing
+2. **Outdated Content** - Update docs when APIs/features change
+3. **Missing Frontmatter** - Pages won't render properly without it
+4. **Build Errors** - Hugo strict mode catches many issues, fix before merge
+
+Documentation PRs should be reviewed for technical accuracy and clarity. When in doubt, ask project maintainers for guidance on organization and content.