graft: clarify in help that `-r` is not just optional Positional parameters are also treated as revisions, but the order of revisions matters and it will often be wrong if the user understands it as `-r` taking multiple revisions as `-r REV1 REV2`. (Alternatively, `-r` could be turned into a no-op flag as the documentation suggests. That would however be less "semantic markup" and I agree with the implementation in 55e7f352b1d3 but not the documentation.)