update intro poster

Author: SerhiiTsybulskyi

docs/Intro.mdx

@@ -31,9 +31,8 @@ import img from './assets/teaser.png';
 
   <hr />
 
-  <a href="https://reachat.dev?utm=reagraph" target="_blank" style={{ background: 'black', padding: 5, borderRadius: 5, position: 'absolute', bottom: 5, right: 5, width: 325 }}>
-    <img src={img} alt="reachat" />
-    Checkout <strong>reachat</strong>, Open-source UI toolkit for building Chat Experiences in React →
+  <a href="https://unifydesignsystem.com/?utm=reagraph" target="_blank" style={{ background: 'black', padding: 5, borderRadius: 5, position: 'absolute', bottom: 5, right: 5, width: 325 }}>
+    <img src={img} alt="Unify design system" />
   </a>
 
   Reagraph is a high-performance network graph visualization built in WebGL for React.