Add .gitlab-ci.yml

.gitlab-ci.yml

+docker-build:
+  image: docker:latest
+  stage: build
+  services:
+    - docker:dind
+  before_script:
+    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+  script:
+    - docker build --pull -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_TAG" .
+    - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_TAG"
+  only:
+    variables: 
+      - '$CI_COMMIT_TAG =~ /^[0-9]+\.[0-9]+\.[0-9]+$/'