README: point at HANDOFF.md, build instructions, license note

README.md

@@ -1,2 +1,25 @@
 # gallery
 
+A high-performance image gallery for Android (primary), Linux and macOS —
+Rust + [Slint](https://slint.dev) 1.18.
+
+**Status: M0 (scaffold).** See **[HANDOFF.md](HANDOFF.md)** — the development
+hand-off with the full plan: architecture, thumbnail pipeline, milestones
+M1–M7, Slint gotchas, permission flow, and performance targets.
+
+## Build
+
+```bash
+./scripts/build.sh debug     # debug x86_64 APK + install on emulator
+./scripts/build.sh           # release x86_64 (emulator)
+./scripts/build.sh aarch64   # release aarch64 (device)
+cargo run                    # desktop (Linux needs libfontconfig1 + pkg-config)
+```
+
+Requires: Rust (rustup), `cargo-apk2`, Android SDK + NDK 27 (see HANDOFF.md §3
+for exact paths/env).
+
+## License
+
+GPL-3.0 (see [LICENSE](LICENSE)). Built on Slint, used under the Slint
+royalty-free license for proprietary apps (see HANDOFF.md §10.4).