How can I add "busybox sh" as init during boot of the custom kernel?

[gmssixty gmssixty]

How can I add "busybox sh" as init during boot of the custom kernel? I
have compiled the kernel and put the bzImage in /dev/sda3 (/mnt/sda3).
Booted that kernel. After booting, I got a message to set the init
process. I have put the busybox in /bin. Now I want to add this
"busybox sh" as an init process. How can I do this?

Note that, I did not install any other software in that /dev/sda3
(/mnt/sda3). I have only bzImage and busybox.