[APIM] Open product discovery

Author: dlepow

articles/api-management/api-management-howto-add-products.md

@@ -181,6 +181,9 @@ After you publish a product, developers can access the APIs. Depending on how th
 
 * **Open product** - Developers can access an open product's APIs without a subscription key. However, you can configure other mechanisms to secure client access to the APIs, including [OAuth 2.0](api-management-howto-protect-backend-with-aad.md), [client certificates](api-management-howto-mutual-certificates-for-clients.md), and [restricting caller IP addresses](./api-management-access-restriction-policies.md#RestrictCallerIPs).
 
+    > [!NOTE]
+    > Open products aren't listed in the developer portal for developers to learn about or subscribe to. They're visible only to the **Administrators** group. You'll need to use another mechanism to inform developers about APIs that can be accessed without a subscription key.
+
     When a client makes an API request without a subscription key:
 
     * API Management checks whether the API is associated with an open product.