Documentation: add pointer to name_to_dev_t for root= values

Update kernel-parameters.txt to point users to the authoritative comment
for name_to_dev_t.  In addition, updates other places where some
name_to_dev_t behavior was discussed.  All other references to root=
appear to be for explicit sample usage or just side comments when
discussing other kernel parameters.

Signed-off-by: Will Drewry <wad@chromium.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/m68k/kernel-options.txt

@@ -129,6 +129,20 @@ decimal 11 is the major of SCSI CD-ROMs, and the minor 0 stands for
 the first of these. You can find out all valid major numbers by
 looking into include/linux/major.h.
 
+In addition to major and minor numbers, if the device containing your
+root partition uses a partition table format with unique partition
+identifiers, then you may use them.  For instance,
+"root=PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF".  It is also
+possible to reference another partition on the same device using a
+known partition UUID as the starting point.  For example,
+if partition 5 of the device has the UUID of
+00112233-4455-6677-8899-AABBCCDDEEFF then partition 3 may be found as
+follows:
+  PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF/PARTNROFF=-2
+
+Authoritative information can be found in
+"Documentation/kernel-parameters.txt".
+
 
 2.2) ro, rw
 -----------