add showcase app screenshot

Author: jaworek

src/docs/resources.md

@@ -2,6 +2,8 @@
 
 A collection of guides, articles, and media to help you build React Native apps for Meta Quest.
 
+[![React Native Developer's Guide to Horizon OS](/screenshots/Card.png)](https://www.callstack.com/ebooks/react-native-developers-guide-to-meta-horizon-os)
+
 ## Guide
 
 - [A Hands-On Path to Bringing React Native Apps to Meta Quest](https://www.callstack.com/ebooks/react-native-developers-guide-to-meta-horizon-os)

src/docs/showcase.md

@@ -6,6 +6,8 @@ A React Native showcase app demonstrating what's possible on Meta Quest.
 
 This showcase app proves React Native's viability for Meta Horizon OS development. Built in just two days, it demonstrates core capabilities and library compatibility.
 
+![Showcase App running on Meta Quest](/screenshots/showcase-app.webp)
+
 ## Features
 
 The app includes: