Add experimental banner (#13)

Author: zenorocha

README.md

@@ -1,7 +1,7 @@
-Note: this SDK is currently in beta and breaking changes may occur. Please create an issue if you come across a bug.
-
 # WorkOS Elixir Library
 
+> **Note:** this an experimental SDK and breaking changes may occur. We don't recommend using this in production since we can't guarantee its stability.
+
 The WorkOS library for Elixir provides convenient access to the WorkOS API from applications written in Elixir.
 
 ## Documentation