There is a screenshot of some of it in the post #29
https://forum.proxmox.com/threads/installing-from-usb-drive-issues.18115/page-2#post-250726
Also, if you use Easy2Boot, this should work...
1. Copy the .ISO file to \_ISO\LINUX on your E2B drive
2. Boot to the proxmox boot menu from the ISO
3...