Description of problem:
When installing a VM through the cockpit from an ISO file stored on the filesystem. The interface should tell the user where to store the ISO file and what permissions should be set.

Version-Release number of selected component (if applicable):
cockpit-machines-184.1-1.el8.noarch

How reproducible:
100%

Steps to Reproduce:
1.Install new VM
2.Set iso destination filesystem
3.Set path to /root/....iso

Actual results:
Installation fails

Expected results:
There is information that the iso cannot be read before the installation starts and what should be set to make it work.

Additional info:
Feel free to move it to documentation if you believe that it should be handled there.