(docs): include in the what's a story documentation an Angular snippet

I re-used a snippet we already had

docs/get-started/whats-a-story.md

@@ -17,6 +17,7 @@ Let’s start with the `Button` component. A story is a function that describes
     'react/button-story.js.mdx',
     'react/button-story.ts.mdx',
     'react/button-story.mdx.mdx',
+    'angular/button-story.ts.mdx',
   ]}
 />