DOC: add InTemporaryDirectory instructions
DOC: add InTemporaryDirectory instructions

Fill out stuff about temporary files.

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