Move your_first_game to a dedicated section, write index.rst

I moved some text from the tutorial to the index.rst document to match
the 3D series and group the overview and pre-requisites there.

getting_started/first_2d_game/index.rst

@@ -0,0 +1,64 @@
+Your first 2D game
+==================
+
+In this step-by-step tutorial series, you will create your first complete 2D
+game with Godot. By the end of the series, you will have a simple yet complete
+game of your own, like the image below.
+
+|image0|
+
+You will learn how the Godot editor works, how to structure a project, and build
+a 2D game.
+
+.. note:: This project is an introduction to the Godot engine. It assumes that
+          you have some programming experience already. If you're new to
+          programming entirely, you should start here: :ref:`doc_scripting`.
+
+The game is called "Dodge the Creeps!". Your character must move and avoid the
+enemies for as long as possible. Here is a preview of the final result:
+
+You will learn to:
+
+- Create a complete 2D game with the Godot editor.
+- Structure a simple game project.
+- Move the player character and change its sprite.
+- Spawn random enemies.
+- Count the score.
+
+And more.
+
+You'll find another series where you'll create a similar game but in 3D. We
+recommend you to start with this one, though.
+
+**Why start with 2D?**
+
+3D games are much more complex than 2D ones. It would be best if you stuck to 2D
+until you understood the game development process and how to use Godot well.
+
+Prerequisites
+-------------
+
+This step-by-step tutorial is intended for beginners who followed the complete
+:ref:`Getting Started <toc-learn-step_by_step>`.
+
+If you're an experienced programmer, you can find the complete demo's source
+code here: `Godot demo projects
+<https://github.com/godotengine/godot-demo-projects>`__.
+
+We prepared some game assets you'll need to download so we can jump straight to
+the code.
+
+You can download them by clicking the link below.
+
+:download:`dodge_assets.zip <files/dodge_assets.zip>`.
+
+Contents
+--------
+
+.. toctree::
+   :maxdepth: 1
+   :name: toc-learn-introduction
+
+   your_first_game.rst
+
+.. |image0| image:: img/dodge_preview.gif

getting_started/step_by_step/your_first_game.rst → getting_started/first_2d_game/your_first_game.rst

@@ -3,27 +3,6 @@
 Your first game
 ===============
 
-Overview
---------
-
-This tutorial will guide you through making your first Godot
-project. You will learn how the Godot editor works, how to structure
-a project, and how to build a 2D game.
-
-.. note:: This project is an introduction to the Godot engine. It
-          assumes that you have some programming experience already. If
-          you're new to programming entirely, you should start here:
-          :ref:`doc_scripting`.
-
-The game is called "Dodge the Creeps!". Your character must move and
-avoid the enemies for as long as possible. Here is a preview of the
-final result:
-
-.. image:: img/dodge_preview.gif
-
-**Why 2D?** 3D games are much more complex than 2D ones. You should stick to 2D
-until you have a good understanding of the game development process and how to
-use Godot.
 
 Project setup
 -------------

index.rst

@@ -77,6 +77,7 @@ The main documentation for the site is organized into the following sections:
 
    getting_started/introduction/index
    getting_started/step_by_step/index
+   getting_started/first_2d_game/index
    getting_started/first_3d_game/index