Introduce experimental OpenAPI shortcode

exampleSite/content.en/docs/content/shortcodes/experimental/openapi.md

@@ -0,0 +1,19 @@
+---
+title: OpenAPI
+---
+
+# OpenAPI
+
+Renders an OpenAPI 3.x specification as a documentation page. Operations are grouped by their first tag.
+
+## Syntax
+
+```tpl
+{{%/* openapi src="spec.json" */%}}
+```
+
+The spec file is loaded via `resources.Get`, so the path is relative to the site's `assets/` directory. JSON and YAML are both supported.
+
+## Example
+
+{{% openapi src="tictactoe.json" %}}