add .gitlab-ci.yml

Ref: #278

.gitlab-ci.yml

@@ -0,0 +1,30 @@
+# from https://gitlab.com/pages/jekyll/-/blob/master/.gitlab-ci.yml
+image: ruby:latest
+
+variables:
+  JEKYLL_ENV: production
+  LC_ALL: C.UTF-8
+
+before_script:
+  - gem install bundler
+  - bundle install
+
+test:
+  stage: test
+  script:
+  - bundle exec jekyll build -d test
+  artifacts:
+    paths:
+    - test
+  rules:
+    - if: $CI_COMMIT_REF_NAME != $CI_DEFAULT_BRANCH
+
+pages:
+  stage: deploy
+  script:
+  - bundle exec jekyll build -d public
+  artifacts:
+    paths:
+    - public
+  rules:
+    - if: $CI_COMMIT_REF_NAME == $CI_DEFAULT_BRANCH