add a note in the migration guide

Author: martinbonnin

docs/source/migration/4.0.mdx

@@ -241,4 +241,6 @@ It is not possible to create a `Schema` from a File or String directly anymore.
 
 ## Removed RxJava artifacts
 
-* Use `toFlow().asFlowable()` and [`kotlinx-coroutines-rx2`](https://github.com/Kotlin/kotlinx.coroutines/tree/master/reactive/kotlinx-coroutines-rx2) or [`kotlinx-coroutines-rx3`](https://github.com/Kotlin/kotlinx.coroutines/tree/master/reactive/kotlinx-coroutines-rx3)
+* Use `toFlow().asFlowable()` and [`kotlinx-coroutines-rx2`](https://github.com/Kotlin/kotlinx.coroutines/tree/master/reactive/kotlinx-coroutines-rx2) or [`kotlinx-coroutines-rx3`](https://github.com/Kotlin/kotlinx.coroutines/tree/master/reactive/kotlinx-coroutines-rx3)
+
+## KotlinLabs 0.1 is not supported anymore