multi arch builds (#26)

build for multiple architects

Co-authored-by: Ruben Momoa <ruben.lobbes@lobbes.nl>
Reviewed-on: #26

.woodpecker/build_release.yml

@@ -44,6 +44,7 @@ steps:
     release_alpine_build_and_publish:
         image: woodpeckerci/plugin-docker-buildx
         settings:
+            platforms: linux/386,linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64/v8,linux/ppc64le,linux/riscv64,linux/s390x
             username: vistanarvas
             password:
                 from_secret: DOCKERHUB_TOKEN