Typo in README.md

This line:
```
echo "k8s_node_type=\"g6-standard-2\"" >> terraform.tfstate
```

Should be:
```
echo "k8s_node_type=\"g6-standard-2\"" >> terraform.tfvars
```

This can be very confusing for users that are familiar with terraform and they can end up with the wrong node type and/or corrupt the terraform state file.
