Landing page links to quickstart tutorial (#3755)

Summary:
Pull Request resolved: #3755

For the next version of Ax we're making "quickstart" the new tutorial entrypoint.

This should be landed **right before** creating the new Ax version.

Reviewed By: mpolson64

Differential Revision: D73938169

fbshipit-source-id: a078bf89f319d4decf1e49c0a603128f42855170

Author: CristianLara

website/src/pages/index.js

@@ -162,7 +162,7 @@ const MyPage = () => {
               Get started
             </Link>
             <Link
-              to="/docs/tutorials/"
+              to="/docs/tutorials/quickstart/"
               className="button button--lg button--outline button--secondary margin--sm">
               Tutorials
             </Link>