Please add usage in README.md

[skrueger8]

Please add a README.md how to use this.

For example:

Requirements: Debian Buster amd64

Steps:

sudo apt install curl debootstrap qemu-user-static qemu-utils u-boot-tools parted
git clone https://github.com/mxOBS/imagebuilder.git
cd imagebuilder
# modify configs/sr-imx8-debian-buster.inc if you want to change anything
sudo ./mktarball.sh configs/sr-imx8-debian-buster.inc
sudo ./mkimage.sh sr-imx8-debian-buster.tar 1024M

# see https://developer.solid-run.com/knowledge-base/i-mx8m-atf-u-boot-and-linux-kernel/ how to create a flash.bin (XXX do we need this step?)
LOOPDEV="$(losetup -f)"
sudo losetup -P -v $LOOPDEV sr-imx8-debian-buster.img
sudo dd if=flash.bin of=/dev/loop0 bs=1024 seek=33
sudo losetup -d $LOOPDEV

See https://developer.solid-run.com/knowledge-base/flashing-an-sd-card/ how to flash the image.