Change developer CTA (#12857)

* change `index.js`

docs/src/pages/index.js

@@ -8,8 +8,8 @@ import styles from "./styles.module.css";
 
 const features = [
   {
-    title: <>⛏ Build an Application</>,
+    title: <>⛏ Build Your First App</>,
-    imageUrl: "apps",
+    imageUrl: "https://github.com/solana-labs/example-helloworld",
     description: <>Get started building your decentralized app or marketplace.</>,
   },
   {