syslinux: fix lack of top level install option
@hertzog I hope this suitably addresses the issue of the syslinux layout missing the top level install entry you raised yesterday.
please note when considering the new layout that there are a couple of commits to be resubmitted that add further accessibility entries, bringing things in sync with the current official install discs. i thought that a detailed consideration of the layout changes could take place in that MR.
from the commit message:
0bf9d2d3 expanded the set of install options, whilst also moving them all to a submenu.
it has since been raised that this is not actually what is wanted, that having an entry for the most common install option is wanted at the top level, like currently with grub2.
this adds such an entry.