This is a problem too -- on Synology. On that specific NAS, Docker can't create directories -- they need to already exist. I believe /volume1/docker/olivetin is a good option. Make sure (using File Station) those directories exist first. Create them if needed. This is required for all containers, and is a Synology-Docker issue.
EDIT: Also, create /volume1/docker/olivetin/data for static-file-server...