Add dockerhub push job

.gitlab-ci.yml

@@ -2,3 +2,14 @@ include:
   - project: jonohill/gitlab-templates
     file: docker.yml
     ref: 62a7636bf2b74ff39266a90528c4540d3276c1f6
+
+variables:
+  DOCKERHUB_REPO: jonoh/docker-buildx-qemu
+
+dockerhub-push:
+  script:
+    - echo "$DOCKERHUB_PASSWORD" | base64 --decode | docker login -u "$DOCKERHUB_USERNAME" --password-stdin
+    - docker tag "$CI_REGISTRY_IMAGE" "$DOCKERHUB_REPO:latest"
+    - docker push "$DOCKERHUB_REPO"
+  only:
+    - master

readme.md

@@ -8,14 +8,14 @@ It's been tested with GitLab CI on gitlab.com, but it should work anywhere that
 This GitLab example should give you an idea of how to use the image.
 
 Dockerfile
-```
+```dockerfile
 FROM alpine
 
 RUN echo "Hello, my CPU architecture is $(uname -m)"
 ```
 
 .gitlab-ci.yml
-```
+```yaml
 variables:
   DOCKER_HOST: tcp://docker:2375/