README.md elaborations on entityAdded and entityRemoved

README.md

@@ -90,9 +90,9 @@ requestAnimationFrame(function () {
 })
 ```
 
-A system is notified when it is added or removed from a World:
+A system is notified when it is added or removed from the world:
 
-```
+```js
 var MySystem = CES.System.extend({
   addedToWorld: function(world)  {
     // Code to handle being added to world. Remeber to call this._super.
@@ -105,15 +105,23 @@ var MySystem = CES.System.extend({
 });
 ```
 
-A World emits signals when entities are added or removed. You can listen for
+The world emits signals when entities are added or removed. You can listen for
 specific entities and handle the signal accordingly:
 
-```
+```js
 var MySystem = CES.System.extend({
   addedToWorld: function(world) {
     world.entityAdded('position', 'velocity').add(function(entity) {
       // This function is called whenever an entity with both 'position' and
-      // 'velocity' components is added to the World.
+      // 'velocity' components is added to the world. It can also be called when
+      // a component is added to an entity; for example, when an entity with
+      // only 'position' has 'velocity' added to it.
+    });
+    world.entityRemoved('position', 'velocity').add(function(entity) {
+      // This function is called whenever an entity with both 'position' and
+      // 'velocity' components is removed from the world. It can also be called 
+      // when a component is removed from an entity; for example, when an entity
+      // with both 'position' and 'velocity' has 'velocity' removed from it.
     });
   }
 });