Update docs on S3 policy to include ListAllMyBuckets permission

This permission is required for `rclone lsd`.

docs/content/s3.md

@@ -351,6 +351,8 @@ permissions are required to be available on the bucket being written to:
 * `PutObject`
 * `PutObjectACL`
 
+When using the `lsd` subcommand, the `ListAllMyBuckets` permission is required.
+
 Example policy:
 
 ```
@@ -373,7 +375,12 @@ Example policy:
               "arn:aws:s3:::BUCKET_NAME/*",
               "arn:aws:s3:::BUCKET_NAME"
             ]
-        }
+        },
+        {
+            "Effect": "Allow",
+            "Action": "s3:ListAllMyBuckets",
+            "Resource": "arn:aws:s3:::*"
+        }	
     ]
 }
 ```