Add build nova doc script

.gitlab-ci.yml

 image: jojomi/hugo
 pages:
         stage: deploy
+        before_script:
+                - apk add --update doxygen
         script:
                 - cd /builds/osy/osy.pages.fel.cvut.cz
+                - sh build-nova-doc.sh
                 - hugo -s hugo -d public
                 - mv hugo/public public
         artifacts:

build-nova-doc.sh

+#!/usr/bin
+set -eu
+(cd nova/kern ; doxygen)
+mv nova/kern/html hugo/static/nova