Fix package name for box64.

[geerlingguy]

I noticed the original instruction suggested installing box64-generic-arm, but that fails now:

jgeerling@ampere-workstation:~$ sudo apt update && sudo apt install box64-generic-arm -y
Hit:2 https://itai-nelken.github.io/weekly-box86-debs/debian  InRelease                                            
Hit:1 https://box64.debian.ryanfortner.dev/debian ./ InRelease                                                     
Hit:3 http://ports.ubuntu.com/ubuntu-ports jammy InRelease                                   
Hit:4 http://ports.ubuntu.com/ubuntu-ports jammy-updates InRelease                
Hit:5 http://ports.ubuntu.com/ubuntu-ports jammy-backports InRelease              
Hit:6 http://ports.ubuntu.com/ubuntu-ports jammy-security InRelease              
Hit:7 https://ppa.launchpadcontent.net/obsproject/obs-studio/ubuntu jammy InRelease
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
4 packages can be upgraded. Run 'apt list --upgradable' to see them.
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
E: Unable to locate package box64-generic-arm

It looks like the package name for generic arm64 is now just box64.