README.md in ka-ching-client-0.3.0 vs README.md in ka-ching-client-0.4.0

- old
+ new

@@ -2,9 +2,13 @@
 
 KaChing::Client is a Ruby API client for the [KaChing Backend project / simonneutert/ka-ching-backend](https://github.com/simonneutert/ka-ching-backend).
 
 [![Ruby](https://github.com/simonneutert/ka-ching-client/actions/workflows/main.yml/badge.svg)](https://github.com/simonneutert/ka-ching-client/actions/workflows/main.yml)
 
+The client is supposed to work with the corresponding backend version. As long as it is `0.x.y` the minor (x in this case) must match. 
+
+---
+
 - [Installation](#installation)
 - [Usage (API V1)](#usage-api-v1)
   - [Setup the client](#setup-the-client)
     - [Customize Faraday](#customize-faraday)
   - [Saldo](#saldo)