change image url param (#7)

diff --git a/README.rst b/README.rst
index 9478886..d1f2146 100644
--- a/README.rst
+++ b/README.rst
@@ -98,6 +98,7 @@
     etcd:
       server:
         engine: kubernetes
+        image: etcd:latest
 
 Copy etcd binary from container
 ---------------