[x86 setup] Document grub < 0.93 as broken

Grub older than 0.93 are broken when the kernel setup is bigger than
8K. This was fixed in 2002, and 0.93 was the first grub version which
fixed this bug.

Signed-off-by: H. Peter Anvin <[e-mail]>

Documentation/Changes

···
 o  procps                 3.2.0                   # ps --version
 o  oprofile               0.9                     # oprofiled --version
 o  udev                   081                     # udevinfo -V
+o  grub                   0.93                    # grub --version
 
 Kernel compilation
 ==================