added initramfs scripts for debian and derivatives

initramfs/Debian/grub-btrfs-overlayfs-boot

@@ -0,0 +1,31 @@
+#!/bin/sh
+
+PREREQ=""
+
+prereqs()
+{
+   echo "$PREREQ"
+}
+
+
+case $1 in
+prereqs)
+   prereqs
+   exit 0
+   ;;
+esac
+
+. /scripts/functions
+
+current_dev=$(resolve_device "${ROOT}")
+
+if [[ $(blkid "${current_dev}" -s TYPE -o value) = "btrfs" ]] && [[ $(btrfs property get ${rootmnt} ro) != "ro=false" ]]; then # run only on a read only snapshot
+	lower_dir=$(mktemp -d -p /)
+	ram_dir=$(mktemp -d -p /)
+	mount --move ${rootmnt} ${lower_dir} # move new_root to lower_dir
+	mount -t tmpfs tmpfs ${ram_dir}
+	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 ${rootmnt}
+fi
+

initramfs/Debian/grub-btrfs-overlayfs-hook

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+. /usr/share/initramfs-tools/hook-functions
+
+manual_add_modules btrfs
+manual_add_modules overlay
+copy_exec $(which btrfs)
+copy_exec $(which btrfsck)
+copy_exec $(which blkid)
+

initramfs/readme.md

@@ -44,6 +44,18 @@ Distributions that use Dracut to make their initramfs (many of the Fedora based
 Grub-btrfs provides the variable `GRUB_BTRFS_SNAPSHOT_KERNEL_PARAMETERS` to add any command to the kernel command line. Set it to `GRUB_BTRFS_SNAPSHOT_KERNEL_PARAMETERS="rd.live.overlay.overlayfs=1"` to make snapshots immutable when booted into. 
 After changing this run `sudo /etc/grub.d/41_snapshots-btrfs` to generate a new snapshot-submenu with the parameter added. 
 
+#### Debian based distros
+
+1. Copy [grub-btrfs-overlayfs-hook](Debian/grub-btrfs-overlayfs-hook) script to initramfs-tools hooks directory:
+`sudo cp grub-btrfs-overlayfs-hook /etc/initramfs-tools/hooks/`
+
+2. Copy [grub-btrfs-overlayfs-boot](Debian/grub-btrfs-overlayfs-boot) script to initramfs-tools local-bottom scripts directory:
+`sudo cp grub-btrfs-overlayfs-boot /etc/initramfs-tools/scripts/local-bottom/`
+
+3. Update your initramfs
+`sudo update-initramfs -u`
+
+
 #### Other distribution
 Refer to your distribution's documentation or contribute to this project to add a paragraph.
 #