voidcannon: support resolving content-id based links

src/content/articles/playground/content.md

@@ -3,11 +3,11 @@
 this is sample text (playground)
 
 ## Test Articles
-- [playground](./playground-test-article)
-- - [playground (partially themed)](./playground-test-article-partial)
-- - [playground (no theme)](./playground-test-article-gm3)
-- [p3](./playground-p3-test-article)
-- [totk](./playground-totk-test-article)
+- [playground](./[playground])
+- - [playground (partially themed)](./[playground-partial])
+- - [playground (no theme)](./[playground-gm3])
+- [p3](./[playground-p3])
+- [totk](./[playground-totk])
 
 <voidcannon-theme-switcher></voidcannon-theme-switcher>
 
@@ -220,6 +220,14 @@ Custom emoji (Persona 3 Reload)
 *   [Link with title](https://www.example.com "Example.com")
 *   <https://www.example.com> (Autolink)
 
+Voidcannon can also resolve content ID based links to their respective slugs:
+
+```md
+[Playground Article](./[playground] "Example")
+```
+
+* [Playground Article](./[playground] "Example")
+
 ## Images
 
 The custom `<voidcannon-harness>` element can be used to render full-width sections.