insert_Rosetta_chainbreaks has an incorrect method signature

[jonlevi]

https://github.com/nrbennet/dl_binder_design/blame/cafa3853ac94dceb1b908c8d9e6954d71749871a/af2_initial_guess/af2_util.py#L251

According to the in-line documentation, this method (insert_Rosetta_chainbreaks in af2_util.py) can take a list of list of indices to insert chainbreaks after. However in reality the method can only take a single index at a time, and thus the arg binderlen is actually of type int and not of type list[int]. It would actually be pretty helpful if the code could be modified to generalize to more than one index at a time, but at the very least maybe just update the documentation to reflect that you can only pass one index at a time for chainbreaks.

Thanks!