This commit adds Documentation/usb/mass-storage.txt file.  It contains
description of how to use the mass storage gadget from user space.  It
elaborates on madule parameters and sysfs interface more then it was
written in the comments in the source code.
Signed-off-by: NMichal Nazarewicz <mina86@mina86.com>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NFelipe Balbi <balbi@ti.com>