docs: Add reference on how to use secrets.json

docker-compose.yml

@@ -5,5 +5,23 @@ services:
     restart: always
     environment:
       POSTGRES_PASSWORD: postgres
+    volumes:
+    - postgres_data:/var/lib/postgresql/data
     ports:
     - 5432:5432
+  mongodb:
+    image: mongo:4.4.6
+    container_name: mongodb
+    restart: unless-stopped
+    environment:
+      MONGO_INITDB_ROOT_USERNAME: username
+      MONGO_INITDB_ROOT_PASSWORD: password
+      MONGO_INITDB_DATABASE: transparenzregister
+    ports:
+    - 27017:27017
+    volumes:
+    - mongo_data:/data/db
+
+volumes:
+  postgres_data:
+  mongo_data: