new entries in PyMdown Extension docs

adds blurbs for 
- superfences
- highlight
- inlinehilite

Author: ntno

documentation/docs/configuration/extensions/pymdown-extensions.md

@@ -63,6 +63,37 @@ See reference for usage:
 
   [Adding Snippets]: ./snippets.md
 
+## SuperFences
+
+The [SuperFences] extension allows fenced blocks to be nested inside block quotes, lists, or other block elements.  Enable it via `mkdocs.yml`:
+
+```yaml
+markdown_extensions:
+  - pymdownx.superfences
+```
+
+This extension is incompatible with the Python Markdown extension `markdown.extensions.fenced_code`.
+
+  [SuperFences]: https://facelessuser.github.io/pymdown-extensions/extensions/superfences/
+
+## Highlight and InlineHilite
+
+The [Highlight] and [InlineHilite] extensions can be used to highlight code blocks.  If used with the [PyMdown SuperFences](#superfences) extension line numbers can be added as well.  Enable them via `mkdocs.yml`:
+
+```yaml
+markdown_extensions:
+  - pymdownx.superfences
+  - pymdownx.highlight
+  - pymdownx.inlinehilite
+```
+
+See reference for recommended configuration options:
+
+- [Code Highlighting > PyMdown and Pygments](../code-highlighting/index.md#pymdown-and-pygments)
+
+  [Highlight]: https://facelessuser.github.io/pymdown-extensions/extensions/highlight/
+  [InlineHilite]: https://facelessuser.github.io/pymdown-extensions/extensions/inlinehilite/
+
 
 # Credit