Document needed permissions in Amazon S3

[rarylson]

I was testing this plugin and the upload funcion doesn't worked.

So, I saw that the app had logged an error saying that some permissions was missing (permission denied error).

Inspecting the source code, I saw that CDN Sync Tool needs the PutObjectAcl permission (in my case, this permission was't really needed, because I was using a public bucket).

My suggestion is adding this example to the documentation:

This plugin needs the following permission to add and sync content in Amazon S3: s3:GetObject, s3:PutObject, s3:DeleteObject, and s3:PutObjectAcl (to the used bucket), and s3:ListAllMyBuckets.