Refactor Nix package definition and enhance README for lidarr-mb-gap

- Updated `flake.nix` to import the new Nix package definition from `nix/package.nix`, streamlining the build process for the lidarr-mb-gap application.
- Enhanced the README.md to include new features such as NixOS module support for automated deployment, detailed deployment instructions, and configuration options for SSH and output directories.
- Added sections for troubleshooting output file issues and clarified the structure of the project, including new files for deployment and web serving.

README.md

@@ -13,6 +13,8 @@ A tool to identify missing albums on MusicBrainz from Deezer releases for artist
 - 🎨 **Interactive HTML Report**: Filter by type (add/update) and by artist
 - 🐍 **Python-based**: Clean, functional codebase with proper logging
 - ❄️ **Nix Support**: Fully packaged with Nix flake for reproducible builds
+- 🚀 **NixOS Module**: Automated deployment with systemd service and timer
+- 🌐 **Web Serving**: Ready for deployment with Caddy or any web server
 
 ## Requirements
 
@@ -58,6 +60,7 @@ LIDARR_API_KEY=your-api-key-here
 # Optional
 SAMBL_URL=https://sambl.lioncat6.com
 MAX_ARTISTS=5  # Limit number of artists processed (0 = no limit)
+OUTPUT_DIR=.  # Directory where output files will be written (default: current directory)
 ```
 
 ### Getting Your Lidarr API Key
@@ -82,7 +85,7 @@ The script will:
 1. Fetch all artists from Lidarr with `monitorNewItems` set to "new" or "all"
 2. For each artist, query SAMBL to find missing albums on MusicBrainz
 3. Generate submission links (a-tisket and Harmony)
-4. Create two output files:
+4. Create two output files in the directory specified by `OUTPUT_DIR` (or current directory):
    - `missing_albums.json` - Machine-readable JSON report
    - `missing_albums.html` - Interactive HTML report with filters
 
@@ -110,7 +113,13 @@ Interactive HTML report with:
 │   ├── main.py              # Main application logic
 │   ├── html_report.py       # HTML report generation
 │   └── pyproject.toml      # Python package configuration
+├── nix/
+│   └── package.nix          # Shared Nix package definition
+├── nixos/
+│   ├── lidarr-mb-gap.nix    # NixOS module for automated deployment
+│   └── DEPLOYMENT.md        # Detailed deployment guide
 ├── flake.nix                # Nix flake definition
+├── Caddyfile                # Caddy configuration for serving reports
 ├── .env                     # Environment variables (create this)
 └── README.md
 ```
@@ -136,6 +145,40 @@ The application uses Python's logging module with systemd-friendly output:
 
 Perfect for running as a systemd service.
 
+## Deployment
+
+### NixOS Automated Deployment
+
+This project includes a NixOS module for automated deployment with:
+- Systemd service for report generation
+- Systemd timer for periodic execution (configurable)
+- Optional automatic rsync sync to VPS
+- SSH key management for secure VPS access
+- Caddy configuration for serving the HTML report
+
+See [nixos/DEPLOYMENT.md](nixos/DEPLOYMENT.md) for detailed deployment instructions.
+
+### Quick Start with NixOS
+
+```nix
+# In your NixOS configuration
+services.lidarr-mb-gap = {
+  enable = true;
+  package = lidarr-mb-gap.packages.${system}.lidarr-mb-gap;  # From flake
+  reportDir = "/var/lib/lidarr-mb-gap/reports";
+  envFile = "/var/lib/lidarr-mb-gap/.env";
+  runInterval = "daily";
+  
+  # Optional: Auto-sync to VPS
+  syncToVPS = true;
+  vpsHost = "user@vps";
+  vpsPath = "/var/www/html";
+  sshKeyFile = "/var/lib/lidarr-mb-gap/.ssh/id_ed25519";
+};
+```
+
+For complete setup instructions, including SSH key configuration and Caddy setup, see the [deployment guide](nixos/DEPLOYMENT.md).
+
 ## Example Output
 
 ```
@@ -166,6 +209,11 @@ Perfect for running as a systemd service.
 - Make sure you're running from the project root
 - If using Nix, ensure the flake is properly built
 
+### Output files not appearing
+- Check that `OUTPUT_DIR` environment variable points to a writable directory
+- Ensure the directory exists and has proper permissions
+- Check logs for any permission errors
+
 ## Contributing
 
 1. Format code with `black src/`