Document chrooting with xchroot

[classabbyamp]

• installation/guides/chroot: use xchroot for chroot install
• installation/guides/fde: use xchroot for install
• installation/musl: use xchroot for glibc chroot
• installation/guides/zfs: change chroot prompt to xchroot format

depends on:

• ~~void-linux/void-packages#37826 merge~~
• void-linux/void-mklive#255 merge and new live images

Should the old documentation of manually setting up the chroot be replaced (as I have currently done) or kept as an alternative method?