add "experimental" status on the readme

Author: Sebastien Stormacq

readme.md

@@ -1,4 +1,6 @@
 
+This package makes it easy to run AWS Lambda Functions written in Swift.
+
 You can read [the Swift AWS Lambda Runtime documentation](https://swiftpackageindex.com/awslabs/swift-aws-lambda-runtime/2.3.0/documentation/awslambdaruntime) on the Swift Package Index.
 
 This guide contains the following sections:
@@ -11,6 +13,8 @@ This guide contains the following sections:
 - [Deploying your Swift Lambda functions](#deploying-your-swift-lambda-functions)
 - [Swift AWS Lambda Runtime - Design Principles](#swift-aws-lambda-runtime---design-principles)
 
+The Swift runtime client is an experimental package. It is subject to change and intended only for evaluation purposes.
+
 ## The Swift AWS Lambda Runtime
 
 Many modern systems have client components like iOS, macOS or watchOS applications as well as server components that those clients interact with. Serverless functions are often the easiest and most efficient way for client application developers to extend their applications into the cloud.