Document the first run's time and logs; say why the VMs use -vga std

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/vm.sh

@@ -67,6 +67,9 @@ vm_start() {
   mkdir -p "$VM_DIR" "$PKG_CACHE"
   VM_PORT="$(free_port)" || die "Couldn't find a free port for the VM's SSH."
 
+  # -vga std, not virtio: on Arch, virtio needs qemu-hw-display-virtio-vga
+  # and qemu-hw-display-virtio-gpu, and with only the first QEMU segfaults
+  # without a message. The VMs are headless (or VNC), so std is enough.
   qemu-system-x86_64 \
     -name coredesktop-smoketest \
     -machine q35,accel=kvm \