Merge pull request #265 from Akrog/bool-required

doc: Remove REQUIRED for boolean values

Author: saad-ali

spec.md

@@ -393,6 +393,8 @@ These limits apply for messages generated by both COs and plugins.
 * A `repeated` or `map` field listed as `REQUIRED` MUST contain at least 1 element.
 * A field noted as `OPTIONAL` MAY be specified and the specification SHALL clearly define expected behavior for the default, zero-value of such fields.
 
+Scalar fields, even REQUIRED ones, will be defaulted if not specified, and any field set to the defaul value will not be serialized over the wire as per [proto3](https://developers.google.com/protocol-buffers/docs/proto3#default).
+
 ### Error Scheme
 
 All CSI API calls defined in this spec MUST return a [standard gRPC status](https://github.com/grpc/grpc/blob/master/src/proto/grpc/status/status.proto).