docs(mkdocs): add pymdownx.highlight and pymdownx.superfences extensions

Used for syntax highlighting in code blocks, and allows for indenting existing code blocks.

References:
- https://squidfunk.github.io/mkdocs-material/setup/extensions/python-markdown-extensions/#highlight
- https://squidfunk.github.io/mkdocs-material/setup/extensions/python-markdown-extensions/#superfences

mkdocs.yml

@@ -41,6 +41,8 @@ theme:
     - toc.follow
 markdown_extensions:
   - admonition
+  - pymdownx.highlight
+  - pymdownx.superfences
 plugins:
   - macros
   - search