Improve README example

README.md

@@ -11,6 +11,7 @@ This library is still very much work-in-progress and not ready for use. It's ava
 
 ```zig
 const std = @import("std");
+
 const flecs = @import("flecs-zig-ble");
 const Context = flecs.Context(void);
 const World = Context.World;
@@ -26,25 +27,35 @@ pub fn main() !void {
     const world = try World.init();
     defer world.deinit();
 
+    // Register components.
     _ = try world.component(Position);
     _ = try world.component(Velocity);
 
-    _ = try world.system("Move", move, flecs.c.EcsOnUpdate, "Position, Velocity");
+    // Register a system that moves any entity that has a `Position` by `Velocity` each update.
+    _ = try world.system("Move", move, flecs.c.EcsOnUpdate, "Position, [in] Velocity");
 
-    const e = world.entity();
+    // Create an entity with both `Position` and `Velocity` already pre-added.
+    const e = try world.entity(.{ .name = "Wroom" }, .{ Position, Velocity });
+    // However the components aren't initialized, so do that here:
     e.set(Position, .{ .x = 10, .y = 20 });
     e.set(Velocity, .{ .x = 1, .y = 2 });
 
+    // Progress the world, updating it forever.
     while (world.progress(0.0)) {  }
 }
 
 fn move(it: Iter) void {
-    const pos_field = it.field(Position, 1);
+    // Entities that share components are stored in the same table.
-    const vel_field = it.field(Velocity, 2);
+    // This function will be called for each table that matches the query.
-
+    // With `field` we can grab a column from this table as a typed slice.
-    for (pos_field, vel_field) |*p, v| {
+    const pos_col = it.field(Position, 1);
-        p.x += v.x;
+    const vel_col = it.field(Velocity, 2);
-        p.y += v.y;
+
+    // Both columns have the same size, so we can iterate them at the same time.
+    // Since we want to modify `Position` we can get a pointer to the element.
+    for (pos_col, vel_col) |*pos, vel| {
+        pos.x += vel.x * it.deltaTime();
+        pos.y += vel.y * it.deltaTime();
     }
 }
 ```