docs: enable syntax highlight for code blocks

Signed-off-by: Jari Kolehmainen <jari.kolehmainen@gmail.com>

mkdocs.yml

@@ -65,6 +65,9 @@ plugins:
   - git-revision-date-localized
 
 markdown_extensions:
+  - pymdownx.highlight: {}
+  - pymdownx.superfences: {}
+  - pymdownx.inlinehilite: {}
   - toc:
       permalink: "#"
       toc_depth: 3