Wrong path to kernel and initrd in documentation

[Brian J. Murrell]

The path to the kernel and initrd on the ISO image, referred to in the documentation is wrong.

https://canonical-subiquity.readthedocs-hosted.com/en/latest/howto/autoinstall-quickstart.html

says to use:

```
kvm -no-reboot -m 2048 \
    -drive file=image.img,format=raw,cache=none,if=virtio \
    -cdrom ~/Downloads/ubuntu-<version-number>-live-server-amd64.iso \
    -kernel /mnt/casper/vmlinuz \
    -initrd /mnt/casper/initrd \
    -append 'autoinstall ds=nocloud-net;s=http://_gateway:3003/'
```

to boot and autoinstall from CD-ROM media. However `/casper/` does not exist on the 22.04 media.

[Brian J. Murrell (brian-interlinx)]

NVM. I was looking at the wrong ISO image.

I cannot see anywhere here that I can close this ticket my self though.