[Feature Request] Create DWARFS Archive From TAR/STDIN

This is a very minor thing, but it would be super useful to add a way to create DWARFS images directly from tar files or from the -O/--to-stdout flag from TAR.

(Sorry if I missed this, I didn't see a mention of it in the readme or a quick search)

Edit:
A bit more explanation for this, as it's likely in order.

If you create a dwarfs image of something that has root owned 600 files as well as non-root owned files you would need root to create the DWARFS archive.

No files, tests, or entry points are named. Start by examining the command-line archive creation flow and how it accepts filesystem input, then clarify the tar/STDIN interface and permission behavior; done should include a documented way to create a DWARFS image without requiring access to root-owned files.

Written by the indexing model from the issue text.