Add usings for slime class and ensure highlighting

Reference feedback MonoGame#56 AristurtleDev#56 (comment)

Author: AristurtleDev

articles/tutorials/building_2d_games/23_completing_the_game/index.md

@@ -291,7 +291,13 @@ Let's implement the input buffering technique we introduced in [Chapter 10](../1
 
 ### Implementing Input Buffering in the Slime Class
 
-To add input buffering for the `Slime` class, we will begin by adding the necessary fields to store our input queue. In the *GameObjects* directory of the *DungeonSlime* project (your main game project), open the *Slime.cs* file and add the following fields after the `_sprite` field:
+For the `Slime` class, we will implement input buffering based on the example given using a `Queue<T>` in [Chapter 10](../10_handling_input/index.md#implementing-a-simple-input-buffer).  In the `GameObject` folder of the `DungeonSlime` project (your main game project), open the `Slime.cs` file so we can make the changes.
+
+First, update the using statements at the top of the `Slime` class so that we can use the `Queue<T>` type:
+
+[!code-csharp[](./snippets/slime/usings.cs?highlight=3)]
+
+Next, add the following fields to the `Slime` class after the `_sprite` field:
 
 [!code-csharp[](./snippets/slime/fields.cs)]
 

articles/tutorials/building_2d_games/23_completing_the_game/snippets/slime/usings.cs

@@ -0,0 +1,6 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.Xna.Framework;
+using MonoGameLibrary;
+using MonoGameLibrary.Graphics;