initrdscripts: Add the simplest init script

When booting from initramfs, one must provide a /init link.
This one is the simplest one, just forking a shell, allowing
for the smallest initramfs.

meta/packages/initrdscripts/files/init-boot.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+mkdir /proc
+mkdir /sys
+mount -t proc proc /proc
+mount -t sysfs sysfs /sys
+
+exec sh