[PATCH] block/stat.txt

I couldn't find any docs explaining the contents of /sys/block/<dev>/stat,
so I wrote up the following.  I'm not completely sure it's accurate - Jens,
could you give a yea or nay on this?

In particular, the counts of read/write IOs and read/write sectors are
incremented in different places - it looks like they both increment as the
request is being finished, but I'm not completely sure of that.

Cc: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>