Allow skullstripped inputs

[mgxd]

Discussed in #306

^{Originally posted by Mak2055 August 10, 2023}
Hello all,

I have some skullstripped data that I would like to analyze using nibabies. When I flag "--skull-strip-t1w skip", I get the response that the skull stripping is currently required. Is there a way of overcoming this issue?

Thank you in advance,
M