feat: add support for mermaid diagrams (#244)

layouts/partials/mermaid.html

@@ -0,0 +1,8 @@
+{{if $.Site.Data.config.enableMermaid}}
+  {{ if .Page.Store.Get "hasMermaid" }}
+    <script type="module">
+      import mermaid from 'https://unpkg.com/mermaid@9/dist/mermaid.esm.min.mjs';
+      mermaid.initialize({ startOnLoad: true });
+    </script>
+  {{ end }}
+{{ end }}