Update file .gitlab-ci.yml

.gitlab-ci.yml

 # This file is a template, and might need editing before it works on your project.
 # Full project: https://gitlab.com/pages/plain-html
 
-image: busybox
+image: python:3.8-alpine
+
+stages:
+  - deploy
 
 pages:
+  tags:
+    - sphinx
   stage: deploy
   script:
-    - echo "The site will be deployed to $CI_PAGES_URL"
+    - python3 -m pip install sphinx rtd
+    - sphinx-build -b html docs/source/ public/
   artifacts:
     paths:
       - public
-  rules:
-    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
+  only:
+    - master