Add .gitlab-ci.yml

.gitlab-ci.yml

+image: docker:stable
+
+stages:
+- build
+
+before_script:
+   - echo -n $CI_JOB_TOKEN | docker login -u gitlab-ci-token --password-stdin $CI_REGISTRY
+
+build:
+  stage: build
+  script:
+    - docker pull $CI_REGISTRY_IMAGE:latest || true
+    - docker build --cache-from $CI_REGISTRY_IMAGE:latest
+      --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHORT_SHA --tag $CI_REGISTRY_IMAGE:latest .
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHORT_SHA
+    - docker push $CI_REGISTRY_IMAGE:latest
\ No newline at end of file