Add flash_livebook.sh to automate Livebook firmware flashing

[mnishiguchi]

Description

Add scripts/flash_livebook.sh, a lightweight shell wrapper that automates the entire process of fetching, provisioning, and flashing the latest Nerves Livebook firmware onto an SD card. It validates prerequisites (bash, curl, fwup), provides a -h|--help usage guide, and cleans up its temporary download directory on exit.

Motivation

Getting started with Nerves Livebook currently requires manually downloading the correct .fw for your MIX_TARGET, entering provisioning options, and burning the image via fwup or Etcher. This script consolidates those steps into a single, self‑documented command, lowering the barrier for newcomers and speeding up iterative demos.

Usage

# Fully interactive run:
./scripts/flash_livebook.sh

# Pre‑set provisioning to skip prompts:
export MIX_TARGET=rpi4
export NERVES_WIFI_SSID="MySSID"
export NERVES_WIFI_PASSPHRASE="MyPass"
export NERVES_SERIAL_NUMBER="pi-42"
./scripts/flash_livebook.sh

By exporting those variables, you skip the corresponding prompts—only SD‑card detection and final confirmation remain interactive.

[lawik]

This looks really nice :)

[fhunleth]

Do you think this section should come first? It seems easier than cloning the repository for a first time user just trying to evaluate the project.

[fhunleth]

I see that you updated it. I didn't mean first overall, but before the detailed way of downloading and running the script. I think that the prerequisites still need to be before it, right?