Adding multiple directories as input

Hello!

Is there any way to specify more than one input directory? Checking the documentation, I found `--filter` but doing it this way involves using the root directory and subsequently ignoring all other subdirectories except the ones you specify, which is somewhat convoluted.

Thank you for DwarFS!

Start by reading the documentation for --filter and the command-line handling of input directories. Determine how multiple input directories should be specified without using the root directory and exclusions; done means the documented invocation accepts the requested directories directly.

Written by the indexing model from the issue text.