Nice work, just installed this and it's cool. I got a couple of suggestions though.
1. Probably need to make it clearer that a prerequisite is having Dynamix System Statistics installed, or perhaps install it as part of your own install routine.
2. I don't use /mnt/user/appdata/ on my array. Instead I use a SSD mounted via unassigned devices, so by installing your plugin I've now got an appdata share on my array of which the only subfolder is vnstat, so I think this should be either configurable by the user, or even grab their current appdata location with something like this.
cat /boot/config/docker.cfg | grep DOCKER_APP_CONFIG_PATH | cut -d'"' -f 2