Update example for policy pack resource

[dboeke]

The current docs for turbot_policy_pack name the policy pack "folder" instead of "pack":

resource "turbot_policy_pack" "folder" {
  parent  = "tmod:@turbot/turbot#/"
  title   = "My Policy Pack"
}

suggest we use

resource "turbot_policy_pack" "pack" {
  parent      = "tmod:@turbot/turbot#/"
  title       = "Demo Policy Pack"
  description = "My Demo Policy Pack"
  akas        = ["my-demo-policy-pack"]
}

Also,

filter should be removed from the Argument Reference as it is not implemented.