Fix ipam-driver name in README to include version tag (:latest)

 README.md

@@ -18,7 +18,7 @@
Then you can use it in newly-created networks:

```bash
docker network create --ipam-driver jacekkow/pyipam new-network
docker network create --ipam-driver jacekkow/pyipam:latest new-network
```

Check out [`test_integration.sh`](test_integration.sh) for more examples.