Added note about the true functionality of Authenticated Users ACL related to S3.

Signed-off-by: Matthew Lapworth <mlapworth@newrelic.com>

README.md

@@ -683,6 +683,7 @@ S3
 -	🔸Eventual data consistency, as discussed above, can be surprising sometimes. If S3 suffers from internal replication issues, an object may be visible from a subset of the machines, depending on which S3 endpoint they hit. Those usually resolve within seconds; however, we’ve seen isolated cases when the issue lingered for 20-30 hours.
 -	🔸**MD5s and multi-part uploads:** In S3, the [ETag header in S3](http://docs.aws.amazon.com/AmazonS3/latest/API/RESTCommonResponseHeaders.html) is a hash on the object. And in many cases, it is the MD5 hash. However, this [is not the case in general](http://stackoverflow.com/questions/12186993/what-is-the-algorithm-to-compute-the-amazon-s3-etag-for-a-file-larger-than-5gb) when you use multi-part uploads. One workaround is to compute MD5s yourself and put them in a custom header (such as is done by [s4cmd](https://github.com/bloomreach/s4cmd)).
 -	🔸**US Standard region:** Previously, the us-east-1 region (also known as the US Standard region) was replicated across coasts, which led to greater variability of latency. Effective Jun 19, 2015 this is [no longer the case](https://forums.aws.amazon.com/ann.jspa?annID=3112). All Amazon S3 Regions now support read-after-write consistency. Amazon S3 also renamed the US Standard Region to the US East (N. Virginia) Region to be consistent with AWS regional naming conventions.
+-	🔸When configuring ACLs on who can access the bucket and contents, an predefined group exists called **Authenticated Users**. This group allows all authenticated users, across all AWS accounts, access to the resource(s). This group is often used, incorrectly, to restrict S3 resource access to authenticated users of the owning account. A typical use case of this ACL is used in conjuction with the [requester pays](http://docs.aws.amazon.com/AmazonS3/latest/dev/RequesterPaysBuckets.html) functionality of S3.
 
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