Update contrib/azurerm/README.md (#6057)

The ansible-playbook needs to ssh-login to Azure virtual machines with
ssh keypair, and users need to specify ssh_public_keys for their own
ssh public key. The change of ssh_public_keys is mandatory.
So this updates contrib/azurerm/README.md to explain that.
In addition, the path of all.yml was wrong. That also is updated with
this.

contrib/azurerm/README.md

@@ -15,8 +15,9 @@ Resource Group. It will not install Kubernetes itself, this has to be done in a
 
 ## Configuration through group_vars/all
 
-You have to modify at least one variable in group_vars/all, which is the **cluster_name** variable. It must be globally
-unique due to some restrictions in Azure. Most other variables should be self explanatory if you have some basic Kubernetes
+You have to modify at least two variables in group_vars/all. The one is the **cluster_name** variable, it must be globally
+unique due to some restrictions in Azure. The other one is the **ssh_public_keys** variable, it must be your ssh public
+key to access your azure virtual machines. Most other variables should be self explanatory if you have some basic Kubernetes
 experience.
 
 ## Bastion host
@@ -59,6 +60,6 @@ It will create the file ./inventory which can then be used with kubespray, e.g.:
 
 ```shell
 $ cd kubespray-root-dir
-$ ansible-playbook -i contrib/azurerm/inventory -u devops --become -e "@inventory/sample/group_vars/all.yml" cluster.yml
+$ ansible-playbook -i contrib/azurerm/inventory -u devops --become -e "@inventory/sample/group_vars/all/all.yml" cluster.yml
 ```