Add information about how arv32.bin is generated

README.md

@@ -53,7 +53,7 @@ The pinout is really simple. On Arduino UNO, it should be:
 > [!WARNING]
 > You should backup all your files, since doing this SD card preparation will destroy your SD card's filesystem.
 - Then you need some tool to directly write a file to SD card. On Windows, you can use [HDD Raw Copy Tool](https://hddguru.com/software/HDD-Raw-Copy-Tool/), on *nix you can use `dd if=file.bin of=/dev/sdX conv=notrunc`.
-- Download the file [`arv32.bin`](https://github.com/raspiduino/arv32-opt/raw/main/rv32.bin) file.
+- Download the file [`arv32.bin`](https://github.com/raspiduino/arv32-opt/raw/main/rv32.bin) file. FYI, this file is generated by dumping `mini-rv32ima` emulator's RAM array to a file when it just finished loading the kernel and stuffs (but has not boot). You can generate your own version for newer updates of Linux kernel or Buildroot.
 - Write it directly to the SD card using the tools in step 2.
 - Now you are done preparing the card.