Update var doc about users accounts (#1685)

docs/vars.md

@@ -129,5 +129,8 @@ The possible vars are:
 
 #### User accounts
 
-Kubespray sets up two Kubernetes accounts by default: ``root`` and ``kube``. Their
-passwords default to changeme. You can set this by changing ``kube_api_pwd``.
+By default, a user with admin rights is created, named `kube`.
+The password can be viewed after deployment by looking at the file
+`PATH_TO_KUBESPRAY/credentials/kube_user`. This contains a randomly generated
+password. If you wish to set your own password, just precreate/modify this
+file yourself or change `kube_api_pwd` var.