docs: Add snapshot_copy

website/docs/r/redshift_cluster.html.markdown

@@ -68,6 +68,7 @@ string.
 * `owner_account` - (Optional) The AWS customer account used to create or copy the snapshot. Required if you are restoring a snapshot you do not own, optional if you own the snapshot.
 * `iam_roles` - (Optional) A list of IAM Role ARNs to associate with the cluster. A Maximum of 10 can be associated to the cluster at any time.
 * `logging` - (Optional) Logging, documented below.
+* `snapshot_copy` - (Optional) Configuration of automatic copy of snapshots from one region to another. Documented below.
 * `tags` - (Optional) A mapping of tags to assign to the resource.
 
 ### Nested Blocks
@@ -79,6 +80,12 @@ string.
 For more information on the permissions required for the bucket, please read the AWS [documentation](http://docs.aws.amazon.com/redshift/latest/mgmt/db-auditing.html#db-auditing-enable-logging)
 * `s3_key_prefix` - (Optional) The prefix applied to the log file names.
 
+#### `snapshot_copy`
+
+* `destination_region` - (Required) The destination region that you want to copy snapshots to.
+* `retention_period` - (Optional) The number of days to retain automated snapshots in the destination region after they are copied from the source region. Defaults to `7`.
+* `grant_name` - (Optional) The name of the snapshot copy grant to use when snapshots of an AWS KMS-encrypted cluster are copied to the destination region.
+
 ## Attributes Reference
 
 The following attributes are exported: