Short lived token help message is incorrect

[russjones]

Problem

When creating a short lived token to add a Trusted Cluster, the help message is incorrect.

$ tctl nodes add --roles=trustedcluster --ttl=1h
The invite token: 3225e0acd379ee3658eaf897a8a568ab
Run this on the new node to join the cluster:
> teleport start --roles=trustedcluster --token=3225e0acd379ee3658eaf897a8a568ab --auth-server=10.12.0.6:3025

Please note:
  - This invitation token will expire in 60 minutes
  - 10.12.0.6:3025 must be reachable from the new node, see --advertise-ip server flag

Even though the help message is incorrect, the token is listed and works correctly.

tctl.sh tokens ls
Token                            Role            Expiry Time (UTC)   
-------------------------------- --------------- ------------------- 
3225e0acd379ee3658eaf897a8a568ab Trustedcluster  29 Dec 17 02:22 UTC 

Proposd Solution

Update the help message to explain that the token should be included in a trusted_cluster resource.