* gnu/system/examples/vm-image.tmpl: New file. * Makefile.am (GUIXSD_VM_SYSTEMS, GUIXSD_VM_IMAGE_BASE, GUIXSD_VM_IMAGE_SIZE): New variables. (release): Add logic to build a VM image. (EXAMPLES): Add 'gnu/system/examples/vm-image.tmpl'. * doc/guix.texi (Running GuixSD in a VM, Installing GuixSD in a VM): Mention the pre-built VM image.