FAQ: Document the error people get if they try to boot the live ISO from BIOS

[ermo]

Some people get puzzled when they see the live ISOs put out a cryptic error message because they're attempting to boot in BIOS mode.

At a minimum, we should document the UEFI requirement in the FAQ, along with showing the outcome of attempting to boot the live ISO using BIOS, so people who read documentation know what to try next.

Suggestion:

If you see this on your screen, it means that you have attempted to boot the live ISO in BIOS mode.
The AerynOS live ISO only supports booting systems using UEFI.

ISOLINUX 6.04 20190226 ETCD Copyright (C) 1994-2015 H. Peter Anvin et al
 
Failed to load ldlinux.c32
Boot failed: press a key to retry...

Example user feedback:

https://github.com/orgs/AerynOS/discussions/139

[CookieSource]

https://aerynos.zulipchat.com/#narrow/channel/543142-Development/topic/UEFI.20only.20message/with/577441579 I'm also working on the issue. But let's add it to our FAQ until that work is finished.