assets: add custom non-bootable disk message

Author: liushuyu

.gitignore

@@ -3,3 +3,4 @@
 /stage
 *.img
 *.fd
+*.bin

assets/non-bootable-msg.txt

@@ -0,0 +1,7 @@
+╔═════════════════════════════════════════════════════════╗
+║ Afterglow: Utility Diskette (DOS, x86)                  ║
+╟─────────────────────────────────────────────────────────╢
+║ This diskette is non-bootable. Please insert the "Boot  ║
+║ Diskette" and then insert this diskette after boot-up.  ║
+╚═════════════════════════════════════════════════════════╝
+Insert "Boot Diskette" and <═╛ to continue ...

lib/assemble.bash

@@ -12,7 +12,9 @@ create_blank_floppy_image() {
     local img_size="$2"
     local img_size_blocks=$((img_size / 1024))
 
-    mkfs.vfat -F12 --mbr=n -n 'AG-BOOT' -C "$img_file" "$img_size_blocks"
+    iconv -t CP437 "${CURDIR}"/assets/non-bootable-msg.txt > "${CURDIR}"/build/non-bootable-msg.bin
+    unix2dos "${CURDIR}"/build/non-bootable-msg.bin
+    mkfs.vfat -F12 --mbr=n -m "${CURDIR}/build/non-bootable-msg.bin" -n 'AG-BOOT' -C "$img_file" "$img_size_blocks"
 }
 
 # $1: floppy disk image file path