chore: experimental readme

Signed-off-by: Thomas Poignant <[email protected]>

Author: thomaspoignant

README.md

@@ -1 +1,5 @@
-# dart-server-sdk
+# dart-server-sdk
+
+![Status](https://img.shields.io/badge/status-experimental-red?style=flat&logo=warning)
+
+:warning: This repository is a work in progress repository for an implementation of the `dart-server-sdk`.