[WebPubSub] Update func sample doc

Clear the runtime version under different function versions.

Author: JialinXin

articles/azure-web-pubsub/quickstart-serverless.md

@@ -381,14 +381,16 @@ Use the following commands to create these items.
     # [JavaScript](#tab/javascript)
 
     ```bash
-    az functionapp create --resource-group WebPubSubFunction --consumption-plan-location <REGION> --runtime node --runtime-version 12 --functions-version 3 --name <FUNCIONAPP_NAME> --storage-account <STORAGE_NAME>
+    az functionapp create --resource-group WebPubSubFunction --consumption-plan-location <REGION> --runtime node --runtime-version 14 --functions-version 3 --name <FUNCIONAPP_NAME> --storage-account <STORAGE_NAME>
     ```
 
     # [C#](#tab/csharp)
 
     ```bash
     az functionapp create --resource-group WebPubSubFunction --consumption-plan-location <REGION> --runtime dotnet --functions-version 3 --name <FUNCIONAPP_NAME> --storage-account <STORAGE_NAME>
     ```
+> [!NOTE]
+> If you're running the function version other than v3.0, please check [Azure Functions runtime versions documentation](../azure-functions/functions-versions.md#languages) to set `--runtime` parameter to supported value.
 
 1. Deploy the function project to Azure: