Update signalr-howto-use-management-sdk.md

Author: Y-Sindo

articles/azure-signalr/signalr-howto-use-management-sdk.md

@@ -62,6 +62,7 @@ Build your instance of `ServiceManager` from a `ServiceManagerBuilder`.
 
 [!INCLUDE [Connection string security comment](includes/signalr-connection-string-security-comment.md)]
 
+
 ``` C#
 
 var serviceManager = new ServiceManagerBuilder()
@@ -90,6 +91,10 @@ Create your instance of `ServiceHubContext` from a `ServiceManager`:
 var serviceHubContext = await serviceManager.CreateHubContextAsync("<Your Hub Name>",cancellationToken);
 ```
 
+> [!NOTE]
+> 
+> Creating `ServiceHubContext` is a rather expensive operation. It's recommended to reuse the same `ServiceHubContext` instance for the same hub.
+
 ### Negotiation
 
 In [default mode](concept-service-mode.md#default-mode), an endpoint `/<Your Hub Name>/negotiate` is exposed for negotiation by Azure SignalR Service SDK. SignalR clients reach this endpoint and then redirect to Azure SignalR Service later.