request: add syslinux bootloader to the live image

[IngeGNUe]

Hi,

I was installing GuixSD on a micro-SD card to test it out without wiping
my current setup, and the grub installation failed, saying that it can't
be installed on "embedded" devices.

I prefer syslinux as a bootloader anyway since configuration is
dead-easy, and I use it on my other systems. I'm hoping you might offer
it as an option on the live image! Currently, running "syslinux
--directory /boot/syslinux/ --install /dev/sdXn" results in "command not
found".

For now, I'll try installing it from within Parabola...

Apart from stty giving i/o errors and having to install the whole thing
using the --fallback switch, I haven't run into any further issues.

Thank you!