Merge pull request #337 from percona/patrickbirch-patch-1

Update xbcloud-s3.md

docs/xbcloud-s3.md

@@ -37,13 +37,15 @@ The following example shows the policy definition for writing to the `xbcloud-te
     "Statement": [
         {
             "Effect": "Allow",
+            "Principal": { "AWS": "*" },
             "Action": [
                 "s3:ListBucket"
             ],
             "Resource": "arn:aws:s3:::xbcloud-testing"
         },
         {
             "Effect": "Allow",
+            "Principal": { "AWS": "*" },
             "Action": [
                 "s3:PutObject",
                 "s3:PutObjectAcl",