Resolves #120 - Add missing ch13 from intro table

Author: SimonDarksideJ

articles/tutorials/building_2d_games/index.md

@@ -46,6 +46,7 @@ This documentation will introduce game development concepts using the MonoGame f
 | [Chapter 10: Handling Input](10_handling_input/index.md)                             | Learn how to handle keyboard, mouse, and gamepad input in MonoGame.                                                                                                                               | [10-Handling-Input](https://github.com/MonoGame/MonoGame.Samples/tree/3.8.4/Tutorials/learn-monogame-2d/src/10-Handling-Input/)                           |
 | [Chapter 11: Input Management](11_input_management/index.md)                         | Learn how to create an input management system to handle keyboard, mouse, and gamepad input, including state tracking between frames and creating a reusable framework for handling player input. | [11-Input-Management](https://github.com/MonoGame/MonoGame.Samples/tree/3.8.4/Tutorials/learn-monogame-2d/src/11-Input-Management/)                       |
 | [Chapter 12: Collision Detection](12_collision_detection/index.md)                   | Learn how to implement collision detection between game objects and handle collision responses like blocking, triggering events, and bouncing.                                                    | [12-Collision-Detection](https://github.com/MonoGame/MonoGame.Samples/tree/3.8.4/Tutorials/learn-monogame-2d/src/12-Collision-Detection/)                 |
+| [Chapter 13: Collision Detection](13_working_with_tilemaps/index.md)                   | This chapter explores tile-based game environments using tilemaps. You will learn how to efficiently create game worlds by arranging tiles from a tileset.                                                    | [13-Tilemap](https://github.com/MonoGame/MonoGame.Samples/tree/3.8.4/Tutorials/learn-monogame-2d/src/13-Tilemap)                 |
 | [Chapter 14: Sound Effects and Music](14_soundeffects_and_music/index.md)            | Learn how to load and play sound effects and background music in MonoGame, including managing audio volume, looping, and handling multiple simultaneous sound effects.                            | [14-SoundEffects-And-Music](https://github.com/MonoGame/MonoGame.Samples/tree/3.8.4/Tutorials/learn-monogame-2d/src/14-SoundEffects-And-Music/)           |
 | [Chapter 15: Audio Controller](15_audio_controller/index.md)                         | Learn how to create a reusable audio controller class to manage sound effects and music, including volume control, muting/unmuting, and proper resource cleanup.                                  | [15-Audio-Controller](https://github.com/MonoGame/MonoGame.Samples/tree/3.8.4/Tutorials/learn-monogame-2d/src/15-Audio-Controller/)                       |
 | [Chapter 16: Working with SpriteFonts](16_working_with_spritefonts/index.md)         | Learn how to create and use SpriteFonts to render text in your MonoGame project, including loading custom fonts and controlling text appearance.                                                  | [16-Working-With-SpriteFonts](https://github.com/MonoGame/MonoGame.Samples/tree/3.8.4/Tutorials/learn-monogame-2d/src/16-Working-With-SpriteFonts/)       |