Add Docker support and GitHub Container Registry CI workflow (#3)

* Add comprehensive Docker support with multi-stage builds
* Set up GitHub Container Registry integration
* Enhance CI/CD workflows with Docker build and push capabilities
* Add --help and --version flags to main application
* Update documentation with Docker usage examples
* Implement security best practices for container deployment

DOCKER.md

@@ -0,0 +1,82 @@
+# Articulate Parser - Docker
+
+A powerful command-line tool for parsing and processing articulate data files, now available as a lightweight Docker container.
+
+## Quick Start
+
+### Pull from GitHub Container Registry
+
+```bash
+docker pull ghcr.io/kjanat/articulate-parser:latest
+```
+
+### Run with Articulate Rise URL
+
+```bash
+docker run --rm -v $(pwd):/data ghcr.io/kjanat/articulate-parser:latest https://rise.articulate.com/share/N_APNg40Vr2CSH2xNz-ZLATM5kNviDIO#/ markdown /data/output.md
+```
+
+### Run with local files
+
+```bash
+docker run --rm -v $(pwd):/data ghcr.io/kjanat/articulate-parser:latest /data/input.json markdown /data/output.md
+```
+
+## Usage
+
+### Basic File Processing
+
+```bash
+# Process from Articulate Rise URL
+docker run --rm -v $(pwd):/data ghcr.io/kjanat/articulate-parser:latest https://rise.articulate.com/share/N_APNg40Vr2CSH2xNz-ZLATM5kNviDIO#/ markdown /data/output.md
+
+# Process a local JSON file
+docker run --rm -v $(pwd):/data ghcr.io/kjanat/articulate-parser:latest /data/document.json markdown /data/output.md
+
+# Process with specific format and output
+docker run --rm -v $(pwd):/data ghcr.io/kjanat/articulate-parser:latest /data/input.json docx /data/output.docx
+```
+
+### Display Help and Version
+
+```bash
+# Show help information
+docker run --rm ghcr.io/kjanat/articulate-parser:latest --help
+
+# Show version
+docker run --rm ghcr.io/kjanat/articulate-parser:latest --version
+```
+
+## Available Tags
+
+-   `latest` - Latest stable release
+-   `v1.x.x` - Specific version tags
+-   `main` - Latest development build
+
+## Image Details
+
+-   **Base Image**: `scratch` (minimal attack surface)
+-   **Architecture**: Multi-arch support (amd64, arm64)
+-   **Size**: < 10MB (optimized binary)
+-   **Security**: Runs as non-root user
+-   **Features**: SBOM and provenance attestation included
+
+## Development
+
+### Local Build
+
+```bash
+docker build -t articulate-parser .
+```
+
+### Docker Compose
+
+```bash
+docker-compose up --build
+```
+
+## Repository
+
+-   **Source**: [github.com/kjanat/articulate-parser](https://github.com/kjanat/articulate-parser)
+-   **Issues**: [Report bugs or request features](https://github.com/kjanat/articulate-parser/issues)
+-   **License**: See repository for license details