response: add module docstring

Author: wprzytula

scylla/src/response/mod.rs

@@ -1,3 +1,12 @@
+//! This module holds entities that represent responses to requests
+//! sent to the cluster by the driver.
+//! The following abstractions are involved:
+//  - [QueryResponse] - a response to any kind of a CQL request.
+//  - [NonErrorQueryResponse] - a non-error response to any kind of a CQL request.
+//! - [QueryResult](query_result::QueryResult) - a result of a CQL QUERY/EXECUTE/BATCH request.
+//! - [QueryRowsResult](query_result::QueryRowsResult) - a result of CQL QUERY/EXECUTE/BATCH
+//!   request that contains some rows, which can be deserialized by the user.
+
 pub mod legacy_query_result;
 pub mod query_result;
 mod request_response;