Only include /bin/sh (not all of /bin) in the chroot

Signed-off-by: Shea Levy <shea@shealevy.com>
Allow specifying packages whose closures should be in the chroot

Signed-off-by: Shea Levy <shea@shealevy.com>
Documentation improvement

Signed-off-by: Shea Levy <shea@shealevy.com>