Replace GitHub link with BETA docs link

Author: ukdaaan

src/content/docs/index.mdx

@@ -11,8 +11,8 @@ hero:
       link: /docs
       icon: right-arrow
       variant: primary
-    - text: Visit us on GitHub!
-      link: https://github.com/setupmd/docs
+    - text: View the BETA docs!
+      link: https://preview.setup.md
       icon: external
 ---