Add basic README.md with an example

README.md

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+# slim
+
+Turning containers into bootable VMs
+
+## Example - Minimal Alpine Busybox
+
+```sh
+# Build the container
+podman build ./example/alpine -t slim-alpine
+
+# Make the container bootable by extracing initrd and vmlinuz (initial ramdisk and kernel)
+slim build slim-alpine
+
+# Boot the image using QEMU, `./example/alpine/init` will drop you into an interactive shell.
+slim run slim-alpine
+
+# Cleanup
+slim image rm slim-alpine
+podman image rm slim-alpine
+```

example/alpine/Containerfile

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+FROM alpine:latest
+RUN mkdir -p /lib/apk/db /run
+RUN apk add --no-cache --initdb linux-virt busybox util-linux
+RUN cp /boot/vmlinuz-virt /vmlinuz && echo "Welcome to slim!" > /etc/motd
+COPY init /init
+RUN chmod +x /init
+

example/alpine/init

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+#!/bin/sh
+
+# Mount special filesystems
+mkdir -p /dev /proc /sys
+[ -c /dev/console ] || mknod -m 600 /dev/console c 5 1
+mount -t proc proc /proc
+mount -t sysfs sysfs /sys
+mount -t devtmpfs dev /dev
+
+# Networking
+echo slim > /proc/sys/kernel/hostname
+modprobe virtio_net
+ip link set lo up 2>/dev/null
+ip link set eth0 up 2>/dev/null
+udhcpc -i eth0 -f -q # Get DHCP lease
+
+echo
+echo 'Welcome to slim!'
+echo
+
+# Run interactive shell
+/bin/sh </dev/console >/dev/console 2>&1
+
+poweroff -f
+while true; do
+    sleep 1
+    poweroff -f
+done