Add example for volume to README

README.md

@@ -4,3 +4,7 @@
 # LimeSurvey Docker
 
 Dockerfile to build a [LimeSurvey](https://limesurvey.org) image for the Docker container platform.
+
+# Persistence
+
+To preserve the uploaded files assign the upload folder into a volume. See *docker-compose.yml* for details.

docker-compose.yml

@@ -4,6 +4,8 @@ services:
     build:
       context: .
       dockerfile: apache/Dockerfile
+    volumes:
+      - /tmp/upload/:/var/www/html/upload/
     links:
       - lime-db
     depends_on: