Fix S3 cache documentation (Amazon's S3 issues)
For Amazon's S3 the ServerAddress should always be s3.amazonaws.com. Minio S3 client will get bucket metadata and modify the URL to point to the valid region (eg. s3-eu-west-1.amazonaws.com) itself.
We should fix the example on Advanced Configuration page and also add a notice about Amazon's S3 URL issue.
Related user's story can be found here: #1198 (closed).