doc: repeated word grub

[Karl Berry]

Hi grubbers,

I just booted a system and got the word "GRUB" being repeated endlessly.
Never seen that before.  I couldn't find this mentioned in the
documentation.  If I'm not missing it, I think a bit of discussion
should be in there.

Searching around (search term: repeated word grub at boot), I see only a
couple references (http://ubuntuforums.org/showthread.php?t=592674),
which are about dual booting Windows.  There is no Windows on my system,
so that's clearly not an absolute requirement, though I don't doubt
that's the most common situation for this error to occur.  Which seems
to be about grub not knowing where to boot everything from.  Or something.

Best,
karl