Outdated description on jgraph/export-server image on Docker hub

[s-geiger-si]

This page on docker hub https://hub.docker.com/r/jgraph/export-server references the compose file under a folder named /standalone, which does not exist: https://github.com/jgraph/docker-drawio/tree/master/image-export/standalone

Also there are no tags for that image, would be nice to have a stable tag in addition to latest.