Docs: add redirect from /usage/introduction to /usage/setup

Co-Authored-By: Craft Agent <agents-noreply@craft.do>

docs/app/usage/introduction/page.tsx

@@ -0,0 +1,12 @@
+"use client";
+
+import { useEffect } from "react";
+import { useRouter } from "next/navigation";
+
+export default function Page() {
+   const router = useRouter();
+   useEffect(() => {
+      router.replace("/usage/setup/");
+   }, [router]);
+   return null;
+}