update changelog

Author: jhunsaker

CHANGELOG.md

@@ -5,6 +5,10 @@ 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).
 
+## [2.6] - 2021-09-28
+- [pyth] filter out quoters far from median
+- [pyth] add linker flags to detect missing defs
+
 ## [2.5] - 2021-09-22
 - [pyth] fixed signed division in conf interval calculation
 - [pyth] enabled stricter compiler flags and fixed associated warnings