Adds chunksize MiB to s3 storage docs

Author: Steven Smith

modules/registry-operator-configuration-resource-overview-aws-s3.adoc

@@ -17,6 +17,10 @@ The image registry `spec.storage.s3` configuration parameter holds the informati
 |Bucket is the bucket name in which you want to store the registry's data.
 It is optional and is generated if not provided.
 
+|`chunkSizeMiB`
+|ChunkSizeMiB is the size of the multipart upload chunks of the S3 API.
+The default is `10` MiB with a minimum of `5` MiB. 
+
 |`region`
 |Region is the AWS region in which your bucket exists. It is optional and is
 set based on the installed AWS Region.