Add Warning-Files to Folders Expected to Be Mounted as Volumes

[hhund]

We should add 'warning' files into folders of the bpe and fhir docker images we expect the user to bind mount. The app could then look for those warning files and display a message bind mount for folder/file 'foo' might be missing or misconfigured to the user on startup if the warning files are readable, assuming that they don't exist if the volume is mounted correctly.