Add CHANGELOG and crate READMEs

- Add CHANGELOG.md documenting 0.1.0 and 0.2.0 releases with contributor
  credits and PR links
- Add README.md to each crate linking to the changelog
- Link READMEs in Cargo.toml files
- Add repository field to -sys crates that were missing it
- Update top-level README to reference changelog and reflect -sys crate split
- Document changelog update step in release process

CHANGELOG.md

@@ -0,0 +1,83 @@
+# 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).
+
+## [0.2.0] - 2026-01-13
+
+### Added
+
+- Workaround for automatic C library input propagation in downstream Nix builds. ([#27] by [@roberth])
+- `EvalStateBuilder::load_ambient_settings()` to control whether global Nix settings are loaded. ([#36] by [@roberth])
+
+### Fixed
+
+- Path coercion failing with "path does not exist" errors due to missing `eval_state_builder_load()` call. ([#36] by [@aanderse])
+
+### Changed
+
+- Split `nix-bindings-util-sys` (which contained all low-level FFI bindings) into separate per-library `*-sys` crates. ([#27] by [@Ericson2314])
+  This allows downstream crates to depend on just the low-level bindings they need without pulling in higher-level crates.
+
+## [0.1.0] - 2026-01-12
+
+Initial release, extracted from the [nixops4 repository](https://github.com/nixops4/nixops4).
+
+### Added
+
+- `nix-bindings-store`: Rust bindings for Nix store operations
+  - Store opening (auto, from URI, from environment)
+  - Store path parsing and manipulation
+  - `Store::get_fs_closure` ([#12] by [@RossComputerGuy], [@roberth])
+  - `Clone` for `Derivation` ([#25] by [@Ericson2314])
+  - Store deduplication workaround for [nix#11979]
+  - aarch64 ABI support ([#26] by [@RossComputerGuy])
+- `nix-bindings-expr`: Rust bindings for Nix expression evaluation
+  - `EvalState` for evaluating Nix expressions
+  - Value creation (int, string, attrs, thunks, primops, etc.)
+  - Value inspection/extraction (`require_*` functions)
+  - Attribute selection and manipulation
+  - Thread registration for GC safety
+- `nix-bindings-fetchers`: Rust bindings for Nix fetchers
+- `nix-bindings-flake`: Rust bindings for Nix flake operations
+  - Flake locking
+  - Flake overriding
+- `nix-bindings-util`: Shared utilities
+  - Context management for Nix C API error handling
+  - Settings access
+- `nix-bindings-util-sys`: Low-level FFI bindings for all Nix C libraries
+
+### Contributors
+
+Thanks to everyone who contributed to the initial development, some of whom may not be listed with individual changes above:
+
+- [@aanderse]
+- [@Ericson2314]
+- [@ErinvanderVeen]
+- [@numinit]
+- [@prednaz]
+- [@Radvendii]
+- [@roberth]
+- [@RossComputerGuy]
+
+<!-- end of 0.1.0 release section -->
+
+[@aanderse]: https://github.com/aanderse
+[@Ericson2314]: https://github.com/Ericson2314
+[@ErinvanderVeen]: https://github.com/ErinvanderVeen
+[@numinit]: https://github.com/numinit
+[@prednaz]: https://github.com/prednaz
+[@Radvendii]: https://github.com/Radvendii
+[@roberth]: https://github.com/roberth
+[@RossComputerGuy]: https://github.com/RossComputerGuy
+
+[#12]: https://github.com/nixops4/nix-bindings-rust/pull/12
+[#25]: https://github.com/nixops4/nix-bindings-rust/pull/25
+[#26]: https://github.com/nixops4/nix-bindings-rust/pull/26
+[#27]: https://github.com/nixops4/nix-bindings-rust/pull/27
+[#36]: https://github.com/nixops4/nix-bindings-rust/pull/36
+[0.2.0]: https://github.com/nixops4/nix-bindings-rust/compare/0.1.0...0.2.0
+[0.1.0]: https://github.com/nixops4/nix-bindings-rust/releases/tag/0.1.0
+[nix#11979]: https://github.com/NixOS/nix/issues/11979