Check links in documentation

issue11409
review390641002

.drone.yml

@@ -36,6 +36,7 @@ pipeline:
         commands:
             - pip install sphinx
             - python -m sphinx -T -E -W -n -b html doc _build/html
+            - python -m sphinx -T -E -W -n -b linkcheck doc _build
         volumes:
             - cache:/root/.cache