docs: add CHANGELOG.md

Author: hgaiser

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).
+
+## [Unreleased]
+
+### Changed
+
+- **Removed `shaderc` dependency** — shaders are now precompiled to SPIR-V and embedded at build time via `include_bytes!`. No `glslc` or Vulkan SDK required to build the crate.
+- **Removed `build.rs`** — no longer needed since shaders are precompiled.
+- **Removed `shader.rs`** — SPIR-V constant and `get_spirv_code()` moved to `pipeline.rs`.
+- **Added `shader/` directory** — contains GLSL source (`color_convert.comp`), compile script (`compile.sh`), precompiled SPIR-V (`color_convert.spv`), and documentation (`README.md`).
+- **Updated README.md** — shader development workflow documented.