Add release build guide

RELEASE.md

@@ -0,0 +1,69 @@
+# Release Build Guide
+
+This document summarizes the release preparation for `dj-cli`.
+
+## Build Targets
+
+The project builds on these platforms:
+
+- **Linux (x86_64-unknown-linux-gnu)**
+- **Windows (x86_64-pc-windows-gnu)**
+- **macOS (x86_64-apple-darwin)** — build requires macOS toolchain and cannot be produced in the current Linux container.
+
+## Prerequisites
+
+- Rust 1.78 or later
+- `yt-dlp` and `ffmpeg` available at runtime
+
+For cross-compiling to Windows on Linux, install the target and toolchain:
+
+```bash
+rustup target add x86_64-pc-windows-gnu
+apt-get update && apt-get install -y mingw-w64
+```
+
+## Build Commands
+
+### Linux
+```bash
+cargo build --release
+```
+Output: `target/release/dj-cli`
+
+### Windows (cross-compiled)
+```bash
+cargo build --release --target x86_64-pc-windows-gnu
+```
+Output: `target/x86_64-pc-windows-gnu/release/dj-cli.exe`
+
+### macOS
+```bash
+cargo build --release --target x86_64-apple-darwin
+```
+> Requires the macOS SDK and linker; cross-compilation failed in this environment because the `cc` linker does not understand `-arch` flags.
+
+## Packaging
+
+Create archives for GitHub release:
+
+```bash
+# Linux tarball
+cd target/release
+ tar czf dj-cli-x86_64-unknown-linux-gnu.tar.gz dj-cli
+
+# Windows zip
+cd target/x86_64-pc-windows-gnu/release
+ zip dj-cli-x86_64-pc-windows-gnu.zip dj-cli.exe
+```
+
+Upload these archives as release assets on GitHub. Include a note that macOS users should build from source or use the Rust crate.
+
+## Tests
+
+Run the test suite before releasing:
+```bash
+cargo test
+```
+
+The current test run completed successfully with zero tests.
+