tck2connectome: Clarify -out_assignments option; add -zero_diagonal option
tck2connectome: Clarify -out_assignments option; add -zero_diagonal option

MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3