Enhance README with API documentation and monitoring details

- Added sections for Swagger API documentation and Prometheus monitoring metrics.
- Included instructions for configuring Prometheus to scrape application metrics.
- Documented available metrics and their descriptions.
- Provided guidelines for adding API documentation using JSDoc and Swagger annotations.

Author: aahnik

README.md

@@ -120,13 +120,45 @@ All test users are created with password: `password123`
 ```bash
 mint/
 ├── app/            # Next.js app router pages
+│   ├── api-doc/    # Swagger API documentation
+│   └── api/       # API routes
 ├── components/     # React components
 ├── db/            # Database schema and migrations
 ├── lib/           # Utility functions and shared logic
+├── middleware/    # Request middleware (logging, metrics, error handling)
 ├── public/        # Static assets
 └── scripts/       # CLI scripts for development
 ```
 
+## Monitoring
+
+The application includes built-in monitoring with Prometheus metrics:
+
+- HTTP request counts and durations
+- Active user counts
+- Database query durations
+
+Metrics are available at: `http://localhost:3000/api/metrics`
+
+### Available Metrics
+
+- `http_requests_total`: Counter of HTTP requests
+- `http_request_duration_ms`: Histogram of HTTP request durations
+- `active_users`: Gauge of currently active users
+- `db_query_duration_ms`: Histogram of database query durations
+
+### Prometheus Configuration
+
+Add to your `prometheus.yml`:
+
+```yaml
+scrape_configs:
+  - job_name: 'mint'
+    static_configs:
+      - targets: ['localhost:3000']
+    metrics_path: '/api/metrics'
+```
+
 ## Troubleshooting
 
 ### Database Issues
@@ -168,4 +200,29 @@ bun db:seed
 
 ## License
 
-This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.
+This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.
+
+## API Documentation
+
+The API documentation is available at `/api-doc` when running the development server.
+It provides:
+
+- Interactive API documentation
+- Request/response examples
+- API endpoint testing interface
+
+### Adding Documentation
+
+Add JSDoc comments with Swagger annotations to your API routes:
+
+```typescript
+/**
+ * @swagger
+ * /api/your-endpoint:
+ *   get:
+ *     summary: Endpoint description
+ *     responses:
+ *       200:
+ *         description: Success response
+ */
+```