add gitlab CI for publishing website

.gitlab-ci.yml

+image: registry.gitlab.com/pages/hugo:latest
+
+variables:
+  GIT_SUBMODULE_STRATEGY: recursive
+
+pages:
+  script:
+  - hugo --config config.toml -D --destination=./public 
+  artifacts:
+    paths:
+    - public
+  only:
+  - master
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