Improve installation process

`meson.build` rewritten with DRY principle. `deploy.sh` added,
which deploys the image on a installation USB stick borrowed from
another project. Image name aligned with the installer's expectations.

deploy.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+device=${1:-}
+if [[ ! -b ${device} ]]; then
+  echo "ERROR: \"${device}\" is not a block device" >&2
+fi
+
+if [[ ! -f build/os.raw ]]; then
+  echo "ERROR: \"build/os.raw\" does not appear to be built, run \"build.sh\"" >&2
+fi
+
+echo 'Copying the image...' >&2
+mnt=$(mktemp --directory)
+mount "${device}2" "${mnt}"
+cp --update "build/os.raw" "${mnt}"
+umount "${mnt}"
+rm -rf "${mnt}"
+echo 'Done.' >&2