Updated for non-custom checkout limitation

Author: chris-nowicki

docs/storefront/stencil/start/index.mdx

@@ -60,13 +60,18 @@ All stencil themes utilize the [Speculation Rules API](https://developer.mozilla
 
 ### Limitations
 
+- Currently only works for non-custom checkout pages.
 - Currently only works if the shopper is using the Google Chrome browser.  Check [browser compatibility](https://developer.mozilla.org/en-US/docs/Web/API/Speculation_Rules_API#browser_compatibility) to see latest browser support.
 - The checkout won't pre-render if the shopper updates their cart on the cart page.
 
 <Callout type="info">
   If you are hosting your own analytics you'll need to make changes to your implementation to ensure compatibility.  See our [hosted analytics documentation](https://developer.bigcommerce.com/docs/integrations/hosted-analytics) for more information.
 </Callout>
 
+<Callout type="info">
+  Custom checkout pages are not supported.  This includes B2B checkout pages and any checkouts that are using the [Checkout SDK](https://developer.bigcommerce.com/docs/storefront/cart-checkout/checkout-sdk).
+</Callout>
+
 ## Blueprint (Legacy framework)