Add Copilot instructions for Unraid plugin documentation

Author: mstrhakr

.github/copilot-instructions.md

@@ -0,0 +1,81 @@
+# Copilot Instructions for unraid-plugin-docs
+
+This is a Jekyll documentation site for Unraid plugin development, hosted on GitHub Pages using the [just-the-docs](https://just-the-docs.github.io/just-the-docs/) theme.
+
+## Project Structure
+
+```
+docs/           # Markdown documentation files (the main content)
+_config.yml     # Jekyll configuration (theme, navigation, collections)
+index.md        # Homepage with Jekyll front matter
+Gemfile         # Ruby dependencies (jekyll ~> 4.3, just-the-docs ~> 0.8)
+```
+
+## Documentation Conventions
+
+### Front Matter for Doc Pages
+All pages in `docs/` should have front matter. The just-the-docs theme uses `nav_order` for menu position:
+
+```yaml
+---
+layout: default
+title: Page Title
+nav_order: 3
+---
+```
+
+### Markdown Style
+- Use `#` for the main title (matches `title` in front matter)
+- Tables for reference information (attributes, commands, events)
+- Code blocks with language hints: ` ```xml `, ` ```php `, ` ```bash `
+- ASCII diagrams for architecture/flow concepts (see `docs/filesystem.md` for examples)
+- Callouts use just-the-docs syntax: `{: .warning }` or `> ⚠️ **Note**:`
+
+### Documenting Unraid Concepts
+When documenting Unraid plugin patterns, include:
+1. **What it is** - Brief explanation
+2. **File/directory location** - Persistence info (USB vs RAM)
+3. **Code example** - Complete, working snippet
+4. **Common patterns** - Real-world usage from existing plugins
+
+## Build & Preview
+
+### Local Development
+```bash
+bundle install           # Install dependencies
+bundle exec jekyll serve # Local preview at http://localhost:4000/unraid-plugin-docs/
+```
+
+### CI/CD Pipeline
+GitHub Actions automatically builds and deploys on push to `main` branch (see `.github/workflows/pages.yml`):
+- **Trigger**: Push to `main` or manual `workflow_dispatch`
+- **Build**: Ruby 3.1, `bundle exec jekyll build`
+- **Deploy**: GitHub Pages artifact deployment
+- **URL**: https://mstrhakr.github.io/unraid-plugin-docs/
+
+Pull requests to `main` should be used for changes; the site rebuilds automatically on merge.
+
+## Key Unraid Concepts Documented
+
+This documentation covers Unraid-specific patterns. When writing or editing:
+
+| Concept | Key Points |
+|---------|-----------|
+| **PLG files** | XML plugin installers with DOCTYPE entities, FILE elements |
+| **Page files** | `.page` files with header/content separator `---` |
+| **Events** | Scripts in `event/` directory, blocking behavior warning |
+| **Persistence** | `/boot/config/plugins/` survives reboot; `/usr/local/emhttp/` is RAM |
+
+## Adding New Documentation Pages
+
+1. Create `docs/new-topic.md` with proper front matter
+2. Add to navigation in the appropriate section (see `index.md` links)
+3. Cross-reference from related pages
+4. Include working code examples from real plugins like `dynamix.*` or `compose.manager`
+
+## External References
+
+Link to real plugin repositories for complex examples:
+- [Dynamix plugins](https://github.com/unraid/dynamix) - Official reference implementation
+- [Community Applications](https://github.com/Squidly271/community.applications) - Complex PHP patterns
+- [Compose Manager](https://github.com/dcflachs/compose_plugin) - Docker integration patterns