update changelog with release info

Author: aldas

CHANGELOG.md

@@ -4,6 +4,20 @@ 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).
 
+## [2.1.1] - 2021-01-26
+
+### Fixed
+
+* `BinaryStreamConnection` endless loop (CPU @ 100%) when stream is ready for reading but stream returns no data at all (#73)
+
+### Added
+
+* Example for Modbus server [examples/example_response_server.php](examples/example_response_server.php)
+
+### Changed
+
+* Changed examples to use `Packet::isCompleteLength()`
+
 ## [2.1.0] - 2020-10-04
 
 ### Added