ah, the classic blind download this script and run, trust us guiz
You can also build from source here: https://github.com/nanovms/nanos && https://github.com/nanovms/ops .
There are also packages available through AUR/homebrew and the like: https://ops.city/downloads .
The script is only there facilitate the 'install' such as ensuring you have qemu installed locally or assessing whether you have kvm/hvf rights/etc.
Also, I don't think this is documented yet but you can target various PRs/builds with ops via this way:
ops run /bin/ls --nanos-version d632de2