Update upgrade guide

website/source/docs/install/upgrade-to-0.6.2.html.md

@@ -70,4 +70,6 @@ In prior versions a bug caused the `bound_iam_role_arn` value in the `aws-ec2`
 authentication backend to actually use the instance profile ARN.  This has been
 corrected, but as a result there is a behavior change. To match using the
 instance profile ARN, a new parameter `bound_iam_instance_profile_arn` has been
-added.
+added. Existing roles will automatically transfer the value over to the correct
+parameter, but the next time the role is updated, the new meanings will take
+effect.