Add notice about ContinueAsNew

Author: cschleiden

README.md

@@ -561,3 +561,7 @@ func Workflow1(ctx workflow.Context) {
 and only if a workflow instance was created with a version of `>= 2` will `Activity3` be executed. Older workflows are persisted with a version `< 2` and will not execute `Activity3`.
 
 This kind of check is understandable for simple changes, but it becomes hard and a source of bugs for more complicated workflows. Therefore for now versioning is not supported and the guidance is to rely on **side-by-side** deployments. See also Azure's [Durable Functions](https://docs.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-versioning) documentation for the same topic.
+
+## `ContinueAsNew`
+
+Both Temporal/Cadence and DTFx support `ContinueAsNew`. This essentially re-starts a running workflow as a new workflow with a new event history. This is needed for long running workflows where the history can become very large, negatively affecting performance. While `WorkflowInstance` supports an `InstanceID` and an `ExecutionID`, this feature is not yet implemented (and might not be).