Basic CI mkdocs build test

.gitlab-ci.yml

+# Basic CI to install and run mkdocs build in strict mode with verbose output
+
+image: registry.gitlab.developers.cam.ac.uk/uis/devops/infra/dockerimages/python
+
+before_script:
+  - pip install mkdocs mkdocs-material
+
+test:
+  script:
+    - mkdocs build -s -v