docs: add Merge custom React component example to custom-react-components page (#5648)

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Devin Logan <devinannlogan@gmail.com>

Author: devin-ai-integration[bot]

fern/products/docs/pages/customization/custom-react-components.mdx

@@ -4,11 +4,21 @@ description: Add custom React components to your Fern docs for interactive, serv
 slug: customization/custom-react-components
 ---
 
-
 You can extend Fern's built-in component library by adding your own custom React components. This allows you to create unique, interactive elements that match your documentation needs. Components are server-side rendered for better SEO and performance, with no layout shifts.
 
+<Frame caption="Merge uses a custom React component to compare feature coverage across integrations in an [interactive matrix](https://docs.merge.dev/merge-unified/hris/integrations/supported-features).">
+  <video
+    src="merge-custom-react.mp4"
+    autoPlay
+    loop
+    playsInline
+    muted
+  >
+  </video>
+</Frame>
+
 <Note title="Defining a constant">
-  Don't use a React component to define a constant. Instead, consider using [reusable snippets](/docs/writing-content/reusable-snippets).
+  Don't use a React component to define a constant. Instead, consider using [reusable snippets](/learn/docs/writing-content/reusable-snippets).
 </Note>
 
 ## Custom components in MDX