docs: 0.21 changelog

Author: matejcik

CHANGELOG.rst

@@ -8,6 +8,31 @@ All notable changes to this project will be documented in this file.
 The format is based on `Keep a Changelog`_, and this project adheres to
 `Semantic Versioning`_.
 
+`0.21`_ - 2024-01-05
+--------------------
+
+.. _0.21: https://github.com/trezor/python-mnemonic/compare/v0.20...v0.21
+
+Added
+~~~~~
+
+- Czech and Portuguese wordlists
+- Option to provide custom list of words instead of loading from built-in file
+
+Changed
+~~~~~~~
+
+- Use `secrets` module for randomness
+- Use English as a default language if none is provided
+- Language detection is unambiguous even if some words are ambiguous
+- Build system switched to Poetry
+
+Removed
+~~~~~~~
+
+- Support for Python below 3.8 was dropped
+
+
 `0.20`_ - 2021-07-27
 ---------------------