cdboot.8: Create a stub manual

[ziaee]

Summary

There's almost nothing here, but that's better than "only imp and jhb
know what this is".

MFC after: 3 days
Reported by: imp, jhb

[imp]

stand/i386/cdboot/cdboot.8

21

It replaces them entirely. Conceptually, it's a first/second stage boot loader for cdrom, just like boot2, gptboot, etc.

[ziaee]

Thats important and makes sense, thank you.
Removed CAVEATS

[ziaee]

I believe this is a simple statement of fact with no copyrightable creative work here, and protected by the copyright of the rest of this work.