Added deprecation banner

Author: KumarVivek

powerapps-docs/developer/common-data-service/online-management-api/sample-quick-start.md

@@ -15,6 +15,9 @@ search.app:
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 # Quick Start Sample: Retrieve Microsoft Dataverse environments using Online Management API 
 
+> [!NOTE]
+> Effective August 26, 2020, the Online Management API is [deprecated](/power-platform/important-changes-coming##online-management-api-powershell-module-and-rest-api-are-deprecated).
+
 The C# sample demonstrates how to authenticate to the Online Management API and then retrieve all Dataverse environments from your Microsoft 365 tenant.
 
 The sample uses the authentication [helper code](sample-authentication-helper.md) to easily authenticate to Online Management API using the OAuth 2.0 protocol and pass in the access token in header of your request.