Add idle_and_physics_processing.rst, write scripting/index.rst

tutorials/scripting/index.rst

@@ -1,6 +1,19 @@
 Scripting
 =========
 
+This section covers programming languages and core features to code your games
+in Godot.
+
+Here, you will find information that is not already covered in more specific
+sections. For instance, to learn about inputs, we recommend you to read
+:ref:`Inputs <toc-learn-features-inputs>`.
+
+Programming languages
+---------------------
+
+The sections below each focus on a given programming language or, in GDNative's
+case, an interface that works with multiple languages.
+
 .. toctree::
    :maxdepth: 1
    :name: toc-learn-scripting
@@ -9,7 +22,20 @@ Scripting
    visual_script/index
    c_sharp/index
    gdnative/index
+
+Core features
+-------------
+
+Some features are specific to the engine and available in all supported
+languages. Whether you code in GDScript, C#, or another language, the pages
+below will help you make the most of Godot.
+
+.. toctree::
+   :maxdepth: 1
+   :name: toc-scripting-core-features
+
    debug/index
+   idle_and_physics_processing
    cross_language_scripting
    creating_script_templates
    change_scenes_manually