ENH: update docstring and remove one copy
ENH: update docstring and remove one copy

bthirion/nipy,alexis-roche/nireg,nipy/nipy-labs,alexis-roche/nipy,alexis-roche/nipy,arokem/nipy,arokem/nipy,arokem/nipy,arokem/nipy,alexis-roche/register,bthirion/nipy,alexis-roche/register,alexis-roche/nipy,alexis-roche/niseg,alexis-roche/nireg,alexis-roche/nipy,alexis-roche/register,bthirion/nipy,bthirion/nipy,nipy/nireg,nipy/nireg,alexis-roche/niseg,nipy/nipy-labs