chroot.md: In fstab, don't set all fs_passno entries to 1 or 2

[camoz]

The docs in chroot.md tell to setup fstab by copying /proc/mounts and then modifying it.

They advise to:

Change the last zero of the entry for / to 1, and the last zero of every other line to 2. These values configure the behaviour of fsck(8).

This is generally not desired for btrfs and xfs filesystems, see fsck.btrfs(8) and
fsck.xfs(8). In addition, f2fs currently seems to have problems with its fsck, so it should be set to 0 here as well (which is what the void-installer is currently doing if it's a root FS).

I also created a PR for the void-installer regarding this: void-linux/void-mklive#229