Add variable for additional backup directories

[w00000dy]

It would be great to have an environment variable that adds different directories to the backup, so I can back up other directories besides the /data directory.

For example, I want to back up my patches in the /patches directory and /data, which I don't think is currently easy to do.

[itzg]

Great idea. I think that'll be pretty easy to add since tar accepts number of input directories.