Update IAM policy in AWS doc

Without this permission, you get the following error:
Failed to regenerate ASG cache: cannot autodiscover ASGs: AccessDenied: User: <arn> is not authorized to perform: autoscaling:DescribeTags because no identity-based policy allows the autoscaling:DescribeTags action.

This is also mentionned by AWS doc: https://docs.aws.amazon.com/eks/latest/userguide/autoscaling.html

cluster-autoscaler/cloudprovider/aws/README.md

@@ -47,6 +47,7 @@ should be updated to restrict the resources/add conditionals:
         "autoscaling:DescribeAutoScalingGroups",
         "autoscaling:DescribeAutoScalingInstances",
         "autoscaling:DescribeLaunchConfigurations",
+        "autoscaling:DescribeTags",
         "ec2:DescribeInstanceTypes",
         "ec2:DescribeLaunchTemplateVersions"
       ],