Add GitLab CI config

.gitlab-ci.yml

+image: alpine:latest
+
+pages:
+  stage: deploy
+  script:
+    - apk add --no-cache nodejs
+    - apk add --no-cache npm
+    - npm install -g pnpm
+    - pnpm install
+    - npm run build
+    - cp -r _site ./public/
+  artifacts:
+    paths:
+      - public
+  only:   
+    - master