docs: add README, changelog, and vim help

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/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [0.1.0] - 2026-04-09
+
+### Added
+
+- Initial release
+- Centered floating progress bar with 60fps smooth animation
+- Post-update results via snacks.nvim picker (ivy layout)
+- Floating markdown fallback when snacks.nvim is unavailable
+- Commit log preview per changed plugin
+- Rollback detection (labels commits when a plugin moves backward)
+- Auto-update cadence: `manual`, `daily`, `weekly`, `monthly`
+- `TinyPackProgress` highlight group (links to `DiagnosticOk` by default)
+- Configurable command name via `command` option
+- `picker` option to force fallback UI for testing
+
+[0.1.0]: https://github.com/swaits/tiny-packupdate.nvim/releases/tag/v0.1.0