Improve EFI example code on Booting Haiku page

[danboid]

Today I configured an old Celeron desktop to multiboot Haiku, Ubuntu and Win10 using GRUB2. I followed these instructions to configure GRUB to boot Haiku:

​https://www.haiku-os.org/guides/booting/

But I thought this line was a bit vague and not well documented:

chainloader ($root)/EFI/BOOT/BOOTX64.EFI

Could we replace that line with a working example like:

chainloader (hd0,1)/EFI/Haiku/BOOTX64.EFI

I had to read the grub docs and search for examples to work out the correct syntax for that statement. In most users cases (hd0,1) will be the correct setting so lets make config a little easier and change the example, or at least explain what ($root) needs to be replaced by.

The existing guide uses /EFI/BOOT/BOOTX64.EFI for the path but that path is likely to already be used for those multibooting hence I think its better to use /EFI/Haiku/BOOTX64.EFI to highlight it is a different BOOTX64.EFI binary to the one installed by Windows, for example.

[nephele]

The example should work, $root is asigned above. Anyhow using grub2 on EFI is a wierd setup, not sure we can do that much about it.