This might be obvious and/or OTT but in order to run the scan sub-command you will need write access to the tag_cache directory. This is slightly different behaviour to the previous where you might redirect the tag_cache to a local file and then manually move it  to some other directory with sudo etc. New (paranoid) users might be less keen to run `sudo mopidy scan`(you could avoid this by overriding the `local/tag_cache_file` option on the command line when you run `mopidy scan`, perhaps that recipe should be suggested/documented?). You might also fine this a bit of a pain when keeping your tag_cache on a remote filesystem that's configured for read-only access. Perhaps it's worthy of some kind of note here.