NF: add example for parcels generator
NF: add example for parcels generator

Small example to show extracting mask for unique ROI values in an image.

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