update doc

[skip ci]

Author: doghappy

CHANGELOG.md

@@ -5,6 +5,13 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [3.1.1] - 2023-09-05
+
+### Added
+
+- Fixed concurrency issue for packet id
+- Upload `SocketIO.Core` and `SocketIO.Serializer.Core` to NuGet
+
 ## [3.1.0] - 2023-08-25
 
 ### Added