Add note that instances termination is asynchronous

Related to Azure/azure-functions-durable-extension#1193

It is not clear from the documentation that the `TerminateAsync` API does not immediately terminate an instance. This PR adds a paragraph clarifying the behavior.

Author: cgillum

articles/azure-functions/durable/durable-functions-instance-management.md

@@ -351,7 +351,7 @@ func durable get-instances --created-after 2018-03-10T13:57:31Z --created-before
 
 If you have an orchestration instance that is taking too long to run, or you just need to stop it before it completes for any reason, you have the option to terminate it.
 
-You can use the `TerminateAsync` (.NET) or the `terminate` (JavaScript) method of the [orchestration client binding](durable-functions-bindings.md#orchestration-client) to terminate instances. The two parameters are an `instanceId` and a `reason` string, which are written to logs and to the instance status. A terminated instance stops running as soon as it reaches the next `await` (.NET) or `yield` (JavaScript) point, or it terminates immediately if it's already on an `await` or `yield`.
+You can use the `TerminateAsync` (.NET) or the `terminate` (JavaScript) method of the [orchestration client binding](durable-functions-bindings.md#orchestration-client) to terminate instances. The two parameters are an `instanceId` and a `reason` string, which are written to logs and to the instance status.
 
 # [C#](#tab/csharp)
 
@@ -386,6 +386,8 @@ See [Start instances](#javascript-function-json) for the function.json configura
 
 ---
 
+A terminated instance will transition into the `Terminated` state. However, this transition will not happen immediately. Rather, the terminate operation will be queued in the task hub along with other operations for that instance. You can use the [instance query](#query-instances) APIs to know when a terminated instance has actually reached the `Terminated` state.
+
 > [!NOTE]
 > Instance termination doesn't currently propagate. Activity functions and sub-orchestrations run to completion, regardless of whether you've terminated the orchestration instance that called them.
 
@@ -794,4 +796,4 @@ func durable delete-task-hub --task-hub-name UserTest
 > [Learn how to handle versioning](durable-functions-versioning.md)
 
 > [!div class="nextstepaction"]
-> [Built-in HTTP API reference for instance management](durable-functions-http-api.md)
+> [Built-in HTTP API reference for instance management](durable-functions-http-api.md)