Add gitlab-ci

.gitignore

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+public

.gitlab-ci.yml

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+image: docker:18
+
+stages:
+  - build
+  - push
+
+before_script:
+  - docker login -u gitlab-ci-token -p $CI_JOB_TOKEN $CI_REGISTRY
+
+Build:
+  stage: build
+  script:
+    - docker pull $CI_REGISTRY_IMAGE:latest || true
+    - >
+      docker build
+      --pull
+      --build-arg GITLAB_USER=gitlab-ci-token
+      --build-arg GITLAB_PASS=$CI_JOB_TOKEN
+      --cache-from $CI_REGISTRY_IMAGE:latest
+      --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+      .
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+
+Push latest:
+  variables:
+    # We are just playing with Docker here. 
+    # We do not need GitLab to clone the source code.
+    GIT_STRATEGY: none
+  stage: push
+  only:
+    # Only "master" should be tagged "latest"
+    - master
+  script:
+    # Because we have no guarantee that this job will be picked up by the same runner 
+    # that built the image in the previous step, we pull it again locally
+    - docker pull $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+    # Then we tag it "latest"
+    - docker tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA $CI_REGISTRY_IMAGE:latest
+    # Annnd we push it.
+    - docker push $CI_REGISTRY_IMAGE:latest
+
+
+
+# Finally, the goal here is to Docker tag any Git tag
+# GitLab will start a new pipeline everytime a Git tag is created, which is pretty awesome
+Push tag:
+  variables:
+    # Again, we do not need the source code here. Just playing with Docker.
+    GIT_STRATEGY: none
+  stage: push
+  only:
+    # We want this job to be run on tags only.
+    - tags
+  script:
+    - docker pull $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+    - docker tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME