I'd like to try archfs or rdiff-backup-fs (as I understand it's same) but can't figure the right command line.

I make (test) backup with command rdiff-backup in-dir out-dir changed/deleted some files and make backup again few times. I was able to find "lost" files but it's hard to do. archfs is a tool to make that easyer but I don't know how to set up. I can't find any examples... just know the commandline to be
rdiff-backup-fs <mount point path> <repository path>
but don't understand parameters.
can someone help me?