adding description of what is used for

aws/globals.go

@@ -1,3 +1,9 @@
 package aws
 
+// A tag used to set custom AWS Tags to resources that do not support `created at` timestamp> - EIP & ECS Clusters.
+// This is used in relation to the `--older-than <duration>` filtering that `cloud-nuke` allows.
+// Due to its destructive nature, `cloud-nuke` has been configured not to delete AWS resources without known creation time,
+// and instead tag them with the `firstSeenTagKey`.
+// The next time `cloud-nuke aws --older-than <duration>` is run, it will use the tag to determine if the AWS resource should be deleted or not.
+
 const firstSeenTagKey = "cloud-nuke-first-seen"