Add changelog

CHANGELOG.md

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+# Changelog
+
+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).
+
+## [1.2.0] - 2023-12-02
+
+### Added
+
+- Like/Unlike buttons to comment notifications to like/unlike comments.
+
+### Changed
+
+- "Subscribe to comments"/"Unsubscribe from comments" buttons now uses the new
+  FreeFeed API for comments notifications.
+
+### Removed
+
+- It is no longer possible to subscribe to comments by sending the bot a link to
+  the post.