add simple boot loader example

bootloader1/boot.asm

@@ -0,0 +1,21 @@
+; boot.asm - prints 'A' and halts
+BITS 16                  ; 16-bit real mode
+ORG 0x7C00               ; boot sector load address
+
+start:
+    mov ah, 0x0E         ; teletype output BIOS function
+    mov al, 'A'          ; character to print
+    mov bh, 0x00         ; page number 0
+    mov bl, 0x07         ; text attribute (light grey on black)
+    int 0x10             ; BIOS video interrupt
+
+    cli                  ; disable interrupts
+hang:
+    hlt                  ; halt CPU
+    jmp hang             ; infinite loop
+
+; fill the rest of the sector with zeros
+times 510-($-$$) db 0     
+
+; boot signature (2 bytes)
+dw 0xAA55