Bump version to 2.0.1.dev0 and update changelog

CHANGELOG.rst

@@ -6,6 +6,8 @@ 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`_.
 
+Unreleased
+----------
 
 `2.0`_ - 2021-12-27
 -------------------

pyproject.toml

 [tool.poetry]
 name = "AlekSIS-App-Resint"
-version = "2.0"
+version = "2.0.1.dev0"
 packages = [
     { include = "aleksis" }
 ]