Update docker-compose.yml

Add app/design volume to allow theme development

docker-compose.yml

@@ -17,6 +17,7 @@ appdata:
     - /srv/www
 #    - ~/.composer:/var/www/.composer
 #    - ./www/app/code:/srv/www/app/code
+#    - ./www/app/design:/srv/www/app/design
 
 phpfpm:
   image: mageinferno/magento2-php:7.0.8-fpm-3