Updated docs with grub

.gitignore

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 *.org
 *.lib
 *.map
+*.iso
 
 makefont
 hankaku.asm

docs/_sidebar.md

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   - [Memory map](memory_map.md)
   - [HRB file format](hrb_format.md)
   - [BPB](bpb.md)
+  - [GRUB](grub.md)
   - [Q&A](Q&A.md)
   - [References](references.md)
 

docs/grub.md

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+# GRUB
+
+## Step-by-Step Guide
+
+1. Prepare the USB Drive with GPT Using fdisk
+
+   1. Open fdisk on the USB Drive:
+
+      ```sh
+      sudo fdisk /dev/sdX
+      ```
+
+   2. Create a New GPT Partition Table:
+
+      Press g to create a new empty GPT partition table.
+      Press n to create a new partition.
+      Press 1 to select the partition number.
+      Press Enter to accept the default first sector.
+      Press Enter again to accept the default last sector (to use the entire drive).
+      Press t to change the partition type.
+      Enter 1 to set the type to EFI (FAT-12/16/32).
+      Press w to write the changes and exit fdisk.
+
+   3. Format the Partition as FAT32:
+
+      ```sh
+      sudo mkfs.vfat -F 32 /dev/sdX1
+      ```
+
+   4. Mount the USB Drive:
+
+      ```sh
+      sudo mkdir -p /mnt/usb
+      sudo mount /dev/sdX1 /mnt/usb
+      ```
+
+2. Write usb.img to a File on the USB Drive
+
+   Copy the usb.img File:
+
+   ```sh
+   sudo cp /path/to/usb.img /mnt/usb/usb.img
+   ```
+
+3. Install GRUB
+
+   1. First, install GRUB and GRUB EFI Modules on your Ubuntu system if it’s not already installed:
+
+      ```sh
+      sudo apt update
+      sudo apt install grub2
+      sudo apt install grub-efi-amd64-bin
+      ```
+
+   2. Install GRUB:
+
+      ```sh
+      sudo grub-install --target=x86_64-efi --efi-directory=/mnt/usb --boot-directory=/mnt/usb/boot --removable
+      ```
+
+4. Configure GRUB
+
+   Create GRUB Configuration:
+
+   ```sh
+   sudo nano /mnt/usb/boot/grub/grub.cfg
+   ```
+
+5. Add the Following Content to grub.cfg:
+
+   ```sh
+   menuentry 'Boot usb.img' {
+       insmod part_gpt
+       insmod fat
+       set root='hd0,gpt1'
+       loopback loop /usb.img
+       chainloader (loop)+1
+   }
+   ```
+
+   Explanation:
+
+   - insmod part_gpt: Load the GPT partition module.
+   - insmod fat: Load the FAT filesystem module.
+   - set root='hd0,gpt1': Set the root device to the first GPT partition on the first hard drive.
+   - loopback loop /usb.img: Create a loopback device for the usb.img file.
+   - chainloader (loop)+1: Chainload the first sector of the loopback device (which should be the boot sector of the usb.img).
+
+6. Unmount the USB Drive
+
+   ```sh
+   sudo umount /mnt/usb
+   ```
+
+7. Test the USB Drive
+
+   Safely Remove the USB Drive.
+   Insert it into Your MacBook Pro and Boot:
+   Hold down the Option (⌥) key during startup.
+   Select the USB drive from the boot menu.