Documentation: maintainer change

I'm dropping off as Documentation/ maintainer.
Rob Landley has agreed to take it over.  Thanks, Rob.

I'll still be around reviewing patches and testing.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: Rob Landley <rob@landley.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>