This special remote type stores file contents in directory on the system.

One use case for this would be if you have a removable drive, that you
cannot put a git repository on for some reason, and you want to use it
to sneakernet files between systems. Just set up both systems to use
the drive's mountpoint as a directory remote.

Setup example:

	# git annex initremote usbdrive directory=/media/usbdrive/