Add hook for buildx xplat builds

[revitteth]

Dockerhub automated build needs a hooks folder with a script which will enable builds for multiple platforms.

[revitteth]

Something like:

#!/bin/bash

Specify the list of platforms to build for

platforms="linux/arm/v7,linux/arm64,linux/amd64"

Ensure that Docker Buildx is installed

docker run --rm --privileged multiarch/qemu-user-static --reset -p yes

Set up Docker Buildx

docker buildx create --name mybuilder
docker buildx use mybuilder

Build the image for multiple platforms using Buildx

docker buildx build --platform $platforms -t myrepo/myimage:latest .