Update readme with submodul command

README.md

@@ -9,10 +9,11 @@ An online deployment of this demo is available at: https://web.villas.fein-aache
 We are using Docker and Docker Compose in order to make it as easy as possible for you to get started.
 
 1. [Install Docker](https://docs.docker.com/engine/installation/).
-2. Download [Demo files](https://git.rwth-aachen.de/VILLASframework/Demo/repository/master/archive.zip) from this repository.
-3. Extract the files.
-4. Open the Docker CLI and navigate to the location of the demo files.
-5. Start demo by running `docker-compose up -d`
+2. Clone repository.
+3. Execute git submodule update --init --recursive
+4. Extract the files.
+5. Open the Docker CLI and navigate to the location of the demo files.
+6. Start demo by running `docker-compose up -d`
 
 ## Backup / Restore Database