[Docker] Fixed so that docker demo usage works again

doc/docker/Dockerfile-demo-vardir

@@ -0,0 +1,14 @@
+FROM busybox
+
+COPY ./web/var /var/www/web/var
+
+WORKDIR /var/www
+
+# Fix permissions for www-data
+RUN chown -R www-data:www-data web/var \
+    && find web/var -type d -print0 | xargs -0 chmod -R 775 \
+    && find web/var -type f -print0 | xargs -0 chmod -R 664
+
+VOLUME ["/var/www/web/var"]
+
+CMD ["/bin/true"]

doc/docker/README.md

@@ -52,6 +52,9 @@ However below environment variable `COMPOSE_FILE` is used instead since this is
 
 ### Production / Demo "image" use
 
+Using this approach, everything will run in containers and volumes. This means that if you for instance upload a image
+using the eZ Platform backend, that image will land in a volume, not somewhere below web/var/ in your project directory.
+
 From root of your projects clone of this distribution, [setup composer auth.json](#composer) and execute the following:
 ```sh
 export COMPOSE_FILE=doc/docker/base-prod.yml
@@ -70,6 +73,8 @@ After some 5-10 seconds you should be able to browse the site on `localhost:8080
 
 ### Development "mount" use
 
+Using this approach, your project directory will be bind mounted into the nginx and php containers. So if you change a
+php file in for instance src/, that change will kick in automatically.
 
 Warning: *Dev setup works a lot faster on Linux then on Windows/Mac where Docker uses virtual machines using shared folders
 by default under the hood, which leads to much slower IO performance.*

doc/docker/demo.yml

@@ -0,0 +1,24 @@
+version: '3.3'
+
+services:
+  app:
+    volumes:
+     - vardir:/var/www/web/var
+    depends_on:
+     - demo-vardir
+
+  web:
+    volumes:
+     - vardir:/var/www/web/var:ro
+
+  demo-vardir:
+    build:
+      context: ../../
+      dockerfile: doc/docker/Dockerfile-demo-vardir
+    volumes:
+     - vardir:/var/www/web/var:ro
+    networks:
+     - backend
+
+volumes:
+  vardir: