Document MTP debugging flag.
Document MTP debugging flag.

cmars/tools,FracturedRetina/go-mtpfs,FracturedRetina/go-mtpfs,riwsakiP8/riwsakiza-go-mtpfs,riwsakiP8/riwsakiza-go-mtpfs,wisavalite/go-mtpfs,cmars/tools,wisavalite/go-mtpfs,wisavalite/go-mtpfs,cmars/tools,riwsakiP8/riwsakiza-go-mtpfs,cmars/tools,FracturedRetina/go-mtpfs