expand top level crate docs slightly and add hello world example

README.md

@@ -5,7 +5,7 @@
 
 ## What is Bevy?
 
-Bevy is a modular game engine built in Rust, with a focus on developer productivity and performance.
+Bevy is an open-source modular game engine built in Rust, with a focus on developer productivity and performance.
 
 ## WARNING
 

bevy_app/src/app_builder.rs

@@ -4,7 +4,7 @@ use crate::{
     stage, App, Events,
 };
 
-use legion::prelude::{Resources, Runnable, Schedulable, Universe, World};
+use legion::prelude::{Resources, Runnable, Schedulable, Universe, World, SystemBuilder, CommandBuffer};
 
 static APP_MISSING_MESSAGE: &str = "This AppBuilder no longer has an App. Check to see if you already called run(). A call to app_builder.run() consumes the AppBuilder's App.";
 
@@ -121,6 +121,15 @@ impl AppBuilder {
         self.add_system_to_stage(stage::UPDATE, system)
     }
 
+    pub fn add_system_fn(&mut self, name: &'static str, system: impl Fn(&mut CommandBuffer) + Send + Sync + 'static) -> &mut Self {
+        let built_system = SystemBuilder::new(name)
+            .build(move |command_buffer, _, _, _| {
+                system(command_buffer);
+            });
+        self.add_system_to_stage(stage::UPDATE, built_system);
+        self
+    }
+
     pub fn add_startup_system_to_stage(
         &mut self,
         stage_name: &str,

examples/hello_world.rs

@@ -0,0 +1,8 @@
+use bevy::prelude::*;
+
+fn main() {
+    App::build()
+        .add_default_plugins()
+        .add_system_fn("hello", |_| println!("hello world!"))
+        .run();
+}

src/lib.rs

@@ -1,13 +1,20 @@
-//! Bevy is a modular game engine built in Rust, with a focus on developer productivity and performance.
-//! 
-//! It has the following design goals:
-//! * Provide a first class user-experience for both 2D and 3D games
-//! * Easy for newbies to pick up, but infinitely flexible for power users
-//! * Fast iterative compile times. Ideally less than 1 second for small to medium sized projects
-//! * Data-first game development using ECS (Entity Component Systems)
-//! * High performance and parallel architecture
-//! * Use the latest and greatest rendering technologies and techniques
-//! 
+//! Bevy is an open-source modular game engine built in Rust, with a focus on developer productivity and performance.
+//!
+//! Check out the [Bevy website](https://bevyengine.org) for more information, read the 
+//! [Bevy Book](https://bevyengine.org/learn/book/introduction) for a step-by-step guide, and [engage with our
+//! community](https://bevyengine.org/community/) if you have any questions or ideas!
+//!  
+//! ```
+//!use bevy::prelude::*;
+//!
+//!fn main() {
+//!    App::build()
+//!        .add_default_plugins()
+//!        .add_system_fn("hello", |_| println!("hello world!"))
+//!        .run();
+//!}
+//! ```
+//!
 //! The "bevy" crate is just a container crate that makes it easier to consume Bevy components.
 //! The defaults provide a "full" engine experience, but you can easily enable / disable features
 //! in your project's Cargo.toml to meet your specific needs. See Bevy's Cargo.toml for a full list of features available.