[PATCH] Updated Documentation/nfsroot.txt

I today booted the first time my embedded device using Linux 2.6.15.2,
which was booted by pxelinux, which then bootet itself from the nfsroot.

This went pretty fine, but when I was reading through
Documentation/nfsroot.txt I saw that there are some more modern versions
available of loading the kernel and passing parameters.

Signed-off-by: Nico Schottelius <nico-kernel@schottelius.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>