MAINTAINERS: Note NFS docs under Documentation/

It struck me while watching Jon Corbet ask how to keep kernel
Documentation up to date, that it might help if we were actually cc'd on
Documentation/filesystems/nfs/ changes.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

MAINTAINERS

@@ -9507,6 +9507,7 @@ F:	include/linux/sunrpc/
 F:	include/uapi/linux/nfsd/
 F:	include/uapi/linux/sunrpc/
 F:	net/sunrpc/
+F:	Documentation/filesystems/nfs/
 
 KERNEL SELFTEST FRAMEWORK
 M:	Shuah Khan <shuah@kernel.org>
@@ -12258,6 +12259,7 @@ F:	include/linux/sunrpc/
 F:	include/uapi/linux/nfs*
 F:	include/uapi/linux/sunrpc/
 F:	net/sunrpc/
+F:	Documentation/filesystems/nfs/
 
 NILFS2 FILESYSTEM
 M:	Ryusuke Konishi <konishi.ryusuke@gmail.com>