Boot on read-only snapshot (#115)

* Create a initramfs folder & configuration files
  * create a initramfs folder
  * create Arch Linux folder
  * Add `HOOK/INSTALL` files to generate a custom initrafms for boot on read-only snapshot for Arch Linux.
  * Add readme file to initramfs folder

* Makefile changes
  * Add readme file
  * Add readme file of initramfs-overlayfs
  * Add HOOK/INSTALL files for Arch Linux

* Readme changes
  * Updates the documentation to be able to boot on a read-only snapshot.
  * Redesign readme again.

initramfs/Arch Linux/overlay_snap_ro-hook

@@ -0,0 +1,15 @@
+#!/usr/bin/ash
+
+run_latehook() {
+	local root_mnt="/new_root"
+	local current_dev=$(resolve_device "$root"); # resolve devices for blkid
+	if [[ $(blkid "${current_dev}" -s TYPE -o value) = "btrfs" ]] && [[ $(btrfs property get ${root_mnt} ro) != "ro=false" ]]; then # run only on a read only snapshot
+		local lower_dir=$(mktemp -d -p /)
+		local ram_dir=$(mktemp -d -p /)
+		mount --move ${root_mnt} ${lower_dir} # move new_root to lower_dir
+		mount -t tmpfs cowspace ${ram_dir}  #meuh!!! space, you can't test !
+		mkdir -p ${ram_dir}/upper
+		mkdir -p ${ram_dir}/work
+		mount -t overlay -o lowerdir=${lower_dir},upperdir=${ram_dir}/upper,workdir=${ram_dir}/work rootfs ${root_mnt}
+	fi
+}

initramfs/Arch Linux/overlay_snap_ro-install

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+build() {
+    add_module btrfs
+    add_module overlay
+    add_binary btrfs
+    add_binary btrfsck
+    add_binary blkid
+    add_runscript
+}
+
+help() {
+    cat <<HELPEOF
+This hook uses overlayfs to boot on a read only snapshot.
+HELPEOF
+}
+
+# vim: set ft=sh ts=4 sw=4 et: