Document application update procedure

README.md

@@ -132,6 +132,31 @@ PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
 
 Replace `/srv/pve-backup-report` with the actual path to the repository. The `cd` is important: Docker Compose finds `compose.yaml` there and the application loads `.env` from it.
 
+### 🔄 Updating the application
+
+Before updating, keep the `.env` file and the `reports/` directory on persistent storage. They must not be replaced by the Docker image.
+
+From the repository directory:
+
+```sh
+git pull
+docker compose build
+docker compose run --rm pve-backup-report --check-config
+docker compose run --rm pve-backup-report --check-api
+```
+
+If the checks pass, run the normal report generation again or wait for the next scheduled execution.
+
+For a local installation without Docker, update the repository and reinstall the application in the virtual environment:
+
+```sh
+git pull
+. .venv/bin/activate
+pip install -r requirements.txt
+pip install -e .
+pve-backup-report --check-config
+```
+
 ## 💻 Direct command-line usage
 
 This mode is useful for development or diagnostics outside a container. The host must have Python, the project's Python dependencies and the system libraries required by WeasyPrint.