some words about storage secret

examples/docker_image/README.md

@@ -6,8 +6,7 @@ You can achieve similar results using the `docker run` command along with its ap
 
 ## Testing the Setup
 
-Modify the `docker-compose.yml` file to reflect your local host user's uid/gid.
-Following this, execute the command:
+Modify the `docker-compose.yml` file to reflect your local host user's uid/gid and then execute the command:
 
 ```bash
 docker compose up
@@ -31,3 +30,8 @@ Consequently, all files generated by NiceGUI (such as the `.nicegui` persistence
 The docker image is designed to relay signals from Docker, such as SIGTERM, to initiate a graceful shutdown of NiceGUI.
 For instance, when you stop the container (using Ctrl+C) and subsequently examine the logs using the `docker compose logs` command,
 you should notice the initiation of the `ui.shutdown` method.
+
+### Storage Secret
+
+In the example `main.py` we read the [storage secret](https://nicegui.io/documentation/storage) from a environment variable.
+This can then be defined in the `docker-compose.yml` (or even passed on from an `.env` file).