Update subscription not-admin copy text (#96)

Author: devin-ai-integration[bot]

app/dashboard/subscription/not-admin.tsx

@@ -1,7 +1,9 @@
 export default async function NotAdmin() {
   return (
     <div className="flex h-full w-full items-center justify-center">
-      <p className="text-sm text-gray-500">Please ask your organization admin to set up a subscription</p>
+      <p className="text-sm text-gray-500">
+        You must be an organization admin to create a new subscription or change an existing one.
+      </p>
     </div>
   );
 }