added a Dockerfile and gitlab-ci config

.gitlab-ci.yml

@@ -0,0 +1,21 @@
+image: egon0/docker-with-buildx-and-git
+
+variables:
+  DOCKER_HOST: tcp://docker:2375/
+  DOCKER_DRIVER: overlay2
+  DOCKER_TLS_CERTDIR: ""
+
+services:
+  - docker:dind
+
+build:
+  stage: build
+  variables:
+    IMAGE_TAG: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG
+    D_IMAGE_TAG: egon0/openwrt-firmware-selector-multiarch:$CI_COMMIT_REF_SLUG
+    D_LATEST_TAG: egon0/openwrt-firmware-selector-multiarch:latest
+  script:
+    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
+    - docker login -u $DOCKER_LOGIN -p $DOCKER_PASSWORD
+    - docker buildx create --use --name A$CI_COMMIT_SHORT_SHA
+    - docker buildx build --platform $BUILD_PLATFORMS --push -t $IMAGE_TAG -t $CI_REGISTRY_IMAGE:latest -t $D_IMAGE_TAG -t $D_LATEST_TAG .