Include the list of allowed values for AWS auto scaling group termination policies (#6710)

Ref: http://docs.aws.amazon.com/autoscaling/latest/userguide/as-instance-termination.html#custom-termination-policy

website/source/docs/providers/aws/r/autoscaling_group.html.markdown

@@ -67,7 +67,7 @@ The following arguments are supported:
 * `load_balancers` (Optional) A list of load balancer names to add to the autoscaling
    group names.
 * `vpc_zone_identifier` (Optional) A list of subnet IDs to launch resources in.
-* `termination_policies` (Optional) A list of policies to decide how the instances in the auto scale group should be terminated.
+* `termination_policies` (Optional) A list of policies to decide how the instances in the auto scale group should be terminated. The allowed values are `OldestInstance`, `NewestInstance`, `OldestLaunchConfiguration`, `ClosestToNextInstanceHour`, `Default`.
 * `tag` (Optional) A list of tag blocks. Tags documented below.
 * `placement_group` (Optional) The name of the placement group into which you'll launch your instances, if any.
 * `metrics_granularity` - (Optional) The granularity to associate with the metrics to collect. The only valid value is `1Minute`. Default is `1Minute`.