Enhanced changelog

Author: semohr

docs/changelog.rst

@@ -2,9 +2,14 @@ Changelog
 ---------
 
 Upcoming
-'''''''
-- Dropped support for Python 3.7 and 3.8
+''''''''
 
+- Dropped support for Python 3.7 and 3.8
+- Added minimal contribution guidelines to CONTRIBUTING.md
+- Changed project linter and formatter from ``flake8`` to ``ruff``. Reformatted 
+    the codebase with ``ruff``.
+- Moved changelog into its own file, ``changelog.rst``. Also added github workflow
+    for automatic changelog reminders.
 
 v0.13.0
 '''''''