[MTD] cmdlineparts documentation change - explain where mtd-id comes from

Signed-off-by: NPhilip Rakity <prakity@yahoo.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/cmdlinepart.c

@@ -7,6 +7,7 @@
  *
  * mtdparts=<mtddef>[;<mtddef]
  * <mtddef>  := <mtd-id>:<partdef>[,<partdef>]
+ *              where <mtd-id> is the name from the "cat /proc/mtd" command
  * <partdef> := <size>[@offset][<name>][ro][lk]
  * <mtd-id>  := unique name used in mapping driver/device (mtd->name)
  * <size>    := standard linux memsize OR "-" to denote all remaining space