Fix EtcdClusterResource invocation in README
`EtcdClusterResource#cluster()` does not exist in current releases. This replaces the example code with the direct call to `#getClientEndpoints()`.
@@ -69,7 +69,7 @@ The `io.etcd:jetcd-launcher` offers a convenient utility to programmatically sta
```java
@Rule public final EtcdClusterResource etcd = new EtcdClusterResource("test-etcd", 1);
-Client client = Client.builder().endpoints(etcd.cluster().getClientEndpoints()).build();
+Client client = Client.builder().endpoints(etcd.getClientEndpoints()).build();
```
This launcher uses the Testcontainers framework.
