Prepare changelog for next release

Author: gonzalocasas

CHANGELOG.rst

@@ -7,6 +7,19 @@ 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>`_.
 
+Unreleased
+----------
+
+**Added**
+
+**Changed**
+
+**Fixed**
+
+**Deprecated**
+
+**Removed**
+
 0.18.2
 ----------