This updates linux/Documentation/usb/proc_usb_info.txt to:

    - refer to "usbfs"
    - describe the /proc/bus/usb/BBB/DDD files
    - more info about the .../drivers and .../devices
    - ... generally, gives more information.
  
This is ever so slightly forward looking in how it describes
bandwidth requirements for high speed periodic transfers,
it's expecting a bugfix patch that's in my queue.  (That info            
is currently broken/meaningless.)