feat: add CHANGELOG.md for documenting notable changes and versioning

Author: CasperKristiansson

CHANGELOG.md

@@ -0,0 +1,26 @@
+# Changelog
+
+All notable changes to **CPython Patch PR Action** will be documented here.  
+The project follows [Semantic Versioning](https://semver.org/) and adheres to the
+[Keep a Changelog](https://keepachangelog.com/en/1.1.0/) format.
+
+## [Unreleased]
+
+### Added
+
+- GitHub Action scaffold with TypeScript build, lint, test, and bundling pipelines.
+- Metadata inputs for `track`, `include_prerelease`, `paths`, `automerge`, `dry_run`,
+  and optional external PR support.
+- Version discovery modules covering CPython tag fetchers, python.org fallback,
+  runner availability checks, track alignment, pre-release guard, and idempotence.
+- Repo scanning engine with glob discovery, pattern matchers, dry-run summaries,
+  targeted rewrite logic, and patch computation.
+- Git automation utilities for branch creation, commits, and duplicate-safe pull
+  requests via Octokit.
+- Initial README, security, contributing, and roadmap documentation optimized for
+  SEO and onboarding.
+
+### Planned
+
+- First tagged release (`v0.x`) once end-to-end automation is validated in sandbox repositories.
+- Automated changelog updates during release workflows.

docs/tasks.md

@@ -171,9 +171,9 @@ Use Context7 MCP for up to date documentation.
         Include minimal and guarded examples, inputs/outputs tables, permissions, FAQs.
         Verify: `actionlint` validates examples.
 
-24. [ ] **CHANGELOG and versioning**
-        Keep `CHANGELOG.md`. Plan `v0.x` then `v1`.
-        Verify: Release notes generated on tag.
+24. [x] **CHANGELOG and versioning**
+       Keep `CHANGELOG.md`. Plan `v0.x` then `v1`.
+       Verify: Release notes generated on tag.
 
 25. [ ] **Action icon and color**
         Update `action.yml` branding.