Add description on QEMU booting

Booting/linux-bootstrap-1.md

@@ -129,6 +129,8 @@ Build and run it with:
 nasm -f bin boot.nasm && qemu-system-x86_64 boot
 ```
 
+This will instruct [QEMU](http://qemu.org) to use the `boot` binary we just built as a disk image. Since the binary generated by the assembly code above fulfills the requirements of the boot sector (the origin is set to 0x7c00, and we end with the magic sequence), QEMU will treat the binary as the master boot record of a disk image.
+
 We will see:
 
 ![Simple bootloader which prints only `!`](http://oi60.tinypic.com/2qbwup0.jpg)