README: stop using ETCDCTL_API=3
Note: v3 has been the default since
@@ -105,8 +105,8 @@ This will bring up etcd listening on port 2379 for client communication and on p
Next, let's set a single key, and then retrieve it:
```
-ETCDCTL_API=3 etcdctl put mykey "this is awesome"
-ETCDCTL_API=3 etcdctl get mykey
+etcdctl put mykey "this is awesome"
+etcdctl get mykey
```
etcd is now running and serving client requests. For more, please check out:
