Desktop build plays music and sound through the system sound output; desktop build documented

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

INSTALL.md

@@ -37,6 +37,22 @@ cp ~/.cargo/registry/src/*/macroquad-*/js/mq_js_bundle.js www/
 python3 -m http.server 8080 -d www   # open http://localhost:8080
 ```
 
+### Desktop build
+
+The game also runs as a native program (Linux, Windows, macOS), without server and multiplayer:
+
+```sh
+cargo build --release
+./target/release/dungeoncraft
+```
+
+On Linux the build needs the ALSA headers (`alsa-lib` / `libasound2-dev`); the sound goes through ALSA (PipeWire and
+PulseAudio take it). The settings, the autosave, the campaign progress and the profile are kept as files in the
+data folder: `~/.local/share/dungeoncraft/` (Linux, or `$XDG_DATA_HOME/dungeoncraft`), `%APPDATA%\DungeonCraft`
+(Windows), `~/Library/Application Support/DungeonCraft` (macOS); `DUNGEONCRAFT_DATA` chooses another one.
+*Save Game* and saved campaigns land in its `saves/` folder; *Load Game* opens the system file dialog there (on
+Linux through the desktop portal), and dropping a file onto the window works as well.
+
 ### Testing the game logic
 
 The tests run natively: a headless simulation of whole games, a savegame round trip, rendering of all music modules and the audio engine: