make explicit that doc is at kubespray.io (#5878)

README.md

@@ -2,7 +2,7 @@
 
 ![Kubernetes Logo](https://raw.githubusercontent.com/kubernetes-sigs/kubespray/master/docs/img/kubernetes-logo.png)
 
-If you have questions, check the [documentation](https://kubespray.io) and join us on the [kubernetes slack](https://kubernetes.slack.com), channel **\#kubespray**.
+If you have questions, check the documentation at [kubespray.io](https://kubespray.io) and join us on the [kubernetes slack](https://kubernetes.slack.com), channel **\#kubespray**.
 You can get your invite [here](http://slack.k8s.io/)
 
 - Can be deployed on **AWS, GCE, Azure, OpenStack, vSphere, Packet (bare metal), Oracle Cloud Infrastructure (Experimental), or Baremetal**