add mention of asynchronous IO

Author: Bulat Shakirzyanov

CHANGELOG.md

@@ -5,5 +5,6 @@ Features:
 * All pre 2.1 Cassandra datatypes, including sets, lists and maps.
 * Simple, prepared and batch statements.
 * Results paging.
+* Asynchronous IO.
 * SSL encryption.
 * Credentials authentication.

README.md

@@ -68,6 +68,7 @@ Features:
 * [All pre 2.1 Cassandra datatypes, including sets, lists and maps](features/datatypes.feature).
 * [Simple](features/simple_statements.feature), [prepared](features/prepared_statements.feature) and [batch statements](features/batch_statements.feature).
 * [Results paging](feature/result_paging.feature).
+* [Asynchronous IO](src/Cassandra/Session.php#L24-L35).
 * [SSL encryption](feature/ssl_encryption.feature).
 * [Credentials authentication](src/Cassandra/Cluster/Builder.php#L312-L320).