add buildx script

buildx.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env sh
+
+REPO=seanauff
+IMAGE=octoprint-klipper
+PLATFORMS="linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64"
+
+docker context use x86_64
+export DOCKER_CLI_EXPERIMENTAL="enabled"
+docker buildx use multiarch-builder
+
+# Build & push latest
+docker buildx build -t ${REPO}/${IMAGE}:latest --compress --push --platform "${PLATFORMS}" .