update readme

README.md

@@ -2,4 +2,44 @@
 
 This is an experimental ECS library intended to be more compiler-friendly. Archetypes are static, and queries are checked at compile-time.
 
-Check out [this blog post](https://nertsal.github.io/blog/so-i-wrote-my-own-ecs/) for a quick intro.
+**Static compiler-checked ECS\***
+
+For an introduction into the idea, see [this blogpost](https://nertsal.github.io/blog/so-i-wrote-my-own-ecs/).
+
+This library attempts to bridge the gap between
+- compile-time guarantees, that are one of the important points of Rust;
+- performance benefits of [SoA](https://en.wikipedia.org/wiki/AoS_and_SoA) (Struct of Array);
+- and ease of use of ECS libraries
+
+*Note: technically this library likely does not qualify as a proper ECS.
+What this library actually is, is a generalized SoA derive
+(For an example of a non-general one, see [soa_derive](https://crates.io/crates/soa_derive) or [soa-rs](https://crates.io/crates/soa-rs/)).
+
+See [crate documentation](todo) for more information.
+
+# Example
+
+[See more examples here](examples/).
+
+```rust
+#[derive(SplitFields)]
+struct Player {
+    position: f64,
+    health: Option<i64>,
+}
+
+struct World {
+    players: StructOf<Vec<Player>>,
+}
+
+let mut world = World { players: Default::default() };
+world.insert(Player {
+    position: 1,
+    health: Some(5),
+});
+
+for (pos, health) in query!(world.players, (&position, &mut health.Get.Some)) {
+    println!("player at {}; health: {}", position, health);
+    *health -= 1;
+}
+```

src/lib.rs

@@ -19,7 +19,7 @@
 //! #[derive(SplitFields)]
 //! struct Player {
 //!     position: f64,
-//!     health: i64,
+//!     health: Option<i64>,
 //! }
 //!
 //! struct World {
@@ -29,10 +29,11 @@
 //! let mut world = World { players: Default::default() };
 //! world.insert(Player {
 //!     position: 1,
-//!     health: 5,
+//!     health: Some(5),
 //! });
 //!
-//! for health in query!(world.players, (&mut health)) {
+//! for (pos, health) in query!(world.players, (&position, &mut health.Get.Some)) {
+//!     println!("player at {}; health: {}", position, health);
 //!     *health -= 1;
 //! }
 //! ```