Document systems aggregator

Author: M1thieu

crates/systems/README.md

@@ -1,3 +1,32 @@
 # Systems
 
-High-level systems including AI, physics solvers, acoustics, and save systems.
+The `systems` workspace crate bundles LP's high-level simulation layers
+(decision-making, acoustics, future MPM integration, and persistence) so they
+can be added to a Bevy app with a single plugin. It sits on top of the domain
+crates (`energy`, `forces`, `information`, `matter`) and takes care of wiring and
+scheduling.
+
+## Modules
+
+- `ai` - utility-driven agency used by LP's creatures and actors.
+- `acoustics` - scaffold for physics-based sound that will hook into matter and
+  wave simulation.
+- `mpm` - placeholder for the upcoming Material Point Method solver.
+- `save_system` - shared save / load infrastructure.
+
+Each module exposes a `prelude` for selective use, while
+`systems::SystemsPlugin` pulls everything together.
+
+## Quick start
+
+```rust
+use bevy::prelude::*;
+use systems::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_plugins(SystemsPlugin::default())
+        .run();
+}
+```