Add an initial page for godot-cpp.

Author: Ivorforce

engine/guidelines/index.rst

@@ -1,3 +1,5 @@
+.. _doc_engine_guidelines:
+
 Engine contribution guidelines
 ==============================
 

index.rst

@@ -80,3 +80,4 @@ for your topic of interest. You can also use the search function in the top-left
    other/website
    other/demos
    other/benchmarks
+   other/godot-cpp

other/godot-cpp.rst

@@ -0,0 +1,40 @@
+Contributing to godot-cpp
+=========================
+
+.. seealso::
+
+    You may also be interested in visiting godot-cpp's official documentation:
+    `C++ (godot-cpp) on the Godot docs <https://docs.godotengine.org/en/latest/tutorials/scripting/cpp/index.html>`__
+
+Thank you for your interest in contributing to `godot-cpp <https://github.com/godotengine/godot-cpp>`__,
+the official C++ GDExtension bindings maintained as part of the Godot project!
+We greatly appreciate help in maintaining and extending this project.
+
+If you wish to help out, ensure you have an account on GitHub and create a "fork" of the
+`godot-cpp repository <https://github.com/godotengine/godot-cpp>`__.
+To contribute, please use our regular :ref:`PR workflow <doc_pr_workflow>`.
+The code should adhere to the same :ref:`code guidelines <doc_engine_guidelines>` as the engine itself.
+
+Please install clang-format and the `pre-commit <https://pre-commit.com/>`__ Python framework so formatting is done
+before your changes are submitted. See the :ref:`code style guidelines <doc_code_style_guidelines>` for instructions.
+
+Feature guidelines
+------------------
+
+godot-cpp's API is modeled after Godot's API. We want writing godot-cpp code to be as similar as possible
+to writing a
+`module <https://docs.godotengine.org/en/latest/contributing/development/core_and_modules/custom_modules_in_cpp.html#doc-custom-modules-in-cpp>`__
+as possible. This means:
+
+* The frameworks (templates, helper methods, etc.) are synchronized to Godot's frameworks regularly.
+* We will not add features that are not already present in Godot. If you want to add new features
+  to godot-cpp's API, please consider proposing the feature to Godot itself first.
+
+If you want to make changes to Godot's API, you can use one of two systems:
+
+* `Core features <https://docs.godotengine.org/en/latest/tutorials/scripting/index.html#core-features>`__: You can add
+  new methods and classes to Godot's core features. This exposes the new functionality on godot-cpp as well.
+  To get started, please see :ref:`doc_intro_to_engine_contributions`.
+* `GDExtension API <https://docs.godotengine.org/en/latest/tutorials/scripting/gdextension/index.html>`__: You can add
+  GDExtension lifecycle methods to the GDExtension API itself. We do not have an article for this kind of change as of
+  yet.