[build] add gitlab ci

.gitlab-ci.yml

+image: alpine:latest
+variables:
+  # This variable will ensure that the CI runner pulls in your theme from the submodule
+  GIT_SUBMODULE_STRATEGY: recursive  
+  # Specify the zola version you want to use here
+  ZOLA_VERSION: "v0.12.0"
+
+pages:
+  script:
+    # Install the zola package from the alpine testing repositories
+    - apk add --update-cache --repository http://dl-3.alpinelinux.org/alpine/edge/testing/ zola
+    # Execute zola build
+    - zola build
+    
+  artifacts:
+    paths:
+      # Path of our artifacts
+      - public
+      
+  # This config will only publish changes that are pushed on the master branch
+  only: 
+    - master