add firmware build script for use with docker

bin/build-firmware.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+sed -i 's/#-DBUILD_EPOCH=$UNIX_TIME/-DBUILD_EPOCH=$UNIX_TIME/' platformio.ini
+
+export PIP_BREAK_SYSTEM_PACKAGES=1
+
+if (echo $2 | grep -q "esp32"); then
+  bin/build-esp32.sh $1
+elif (echo $2 | grep -q "nrf52"); then
+  bin/build-nrf52.sh $1
+elif (echo $2 | grep -q "stm32"); then
+  bin/build-stm32.sh $1
+elif (echo $2 | grep -q "rpi2040"); then
+  bin/build-rpi2040.sh $1
+else
+  echo "Unknown target $2"
+  exit 1
+fi