docs: update README with new link for AI Platform API

PiperOrigin-RevId: 487676461

Author: vertex-sdk-bot

README.rst

@@ -37,7 +37,7 @@ In order to use this library, you first need to go through the following steps:
 
 .. _Select or create a Cloud Platform project.: https://console.cloud.google.com/project
 .. _Enable billing for your project.: https://cloud.google.com/billing/docs/how-to/modify-project#enable_billing_for_a_project
-.. _Enable the Vertex AI API.:  https://cloud.google.com/ai-platform/docs
+.. _Enable the Vertex AI API.:  https://cloud.google.com/vertex-ai/docs/start/use-vertex-ai-python-sdk
 .. _Setup Authentication.: https://googleapis.dev/python/google-api-core/latest/auth.html
 
 Installation