MAINTAINERS: add web link for nilfs project

Add nilfs.osdn.jp as the second web site of nilfs project.

Link: http://lkml.kernel.org/r/1461935747-10380-6-git-send-email-konishi.ryusuke@lab.ntt.co.jp


Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>