Sorry, but I missed the ISO part in my original reply. Normally, one would add an entry to fstab to make a mount permanent, such as if you had an external hard drive that could be removed but usually wasn't.
The mkisofs is a little different. It creates an iso image that is stored in your current working directory.
I think in order to do this you would need to make a short script file (starting with #!/bin/sh) that has that command in it. Then call that script file from one a locations such as rc.local that is called upon start up.