Update Readme for k8s 1.9

this flag or `--discovery-token-ca-cert-hash` needs to be set since 1.9
https://github.com/kubernetes/kubeadm/blob/master/docs/design/design_v1.9.md#shared-token-discovery

Signed-off-by: Robin Winkelewski <[email protected]>

Author: w9n

README.md

@@ -74,9 +74,9 @@ To boot a node use:
 
 More specifically, to start 3 nodes use 3 separate shells and run this:
 ```
-shell1> ./boot.sh 1 --token bb38c6.117e66eabbbce07d 192.168.65.22:6443
-shell2> ./boot.sh 2 --token bb38c6.117e66eabbbce07d 192.168.65.22:6443
-shell3> ./boot.sh 3 --token bb38c6.117e66eabbbce07d 192.168.65.22:6443
+shell1> ./boot.sh 1 --token bb38c6.117e66eabbbce07d 192.168.65.22:6443 --discovery-token-unsafe-skip-ca-verification
+shell2> ./boot.sh 2 --token bb38c6.117e66eabbbce07d 192.168.65.22:6443 --discovery-token-unsafe-skip-ca-verification
+shell3> ./boot.sh 3 --token bb38c6.117e66eabbbce07d 192.168.65.22:6443 --discovery-token-unsafe-skip-ca-verification
 ```
 
 ## Platform specific information