Add instance_type bug to troubleshooting guide

[jfomhover]

When users do not create the instance_type in AKS, they will see an exception:

AML Kubernetes Compute job failed. 9: {"Msg":"Invalid instance type. The instance type defined resource requirement has exceeded the node size. Please ask your admin to modify the instance type resource definition or use another instance type.","Code":9}

we should document that in our TSG, with links to the appropriate steps.