Added note re ip_forward and updated dashboard url

[chrisbu]

Description

For my install (raspbian buster) I had to also set net.ipv4.ip_forward=1 to get networking working between nodes.
Also updated the alternative dashboard url to the current one.

Motivation and Context

Fixed problems accessing dashboard when it was deployed anywhere other than the master node.

• I have raised an issue to propose this change (required)

How Has This Been Tested?

Tested using raspbian buster fresh install and a 3 node cluster. Not tested on earlier versions of raspbian.

Types of changes

• [ x] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ x] My code follows the code style of this project.
• [ x] I have tested this change and prove it works
• [ x] I've read the CONTRIBUTION guide
• [ x] I have signed-off my commits with git commit -s

[addynaikvh]

Typo.. duplicate kubectl

[davelosert]

@chrisbu : Just stumbled accross this PR when I was trying to install the dashboard.
You might also want to adjust the ClusterRoleBinding above to:

apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: kubernetes-dashboard-admin
  labels:
    k8s-app: kubernetes-dashboard
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cluster-admin
subjects:
- kind: ServiceAccount
  name: kubernetes-dashboard
  namespace: kubernetes-dashboard