Reorganize documentation for contributors

- Merge Community/Contributing and Engine Development into one top-level section, Contributing.
- Structure it in a way that gives equal priority to various ways to contribute, including documentation.
- Rename several articles to be more comprehensive and in line with the overall state of the documentation.
- Rewrite the guide for class reference contributions.

contributing/development/debugging/vulkan/index.rst

@@ -0,0 +1,8 @@
+Vulkan
+======
+
+.. toctree::
+   :maxdepth: 1
+   :name: toc-devel-vulkan
+
+   vulkan_validation_layers

contributing/development/debugging/vulkan/vulkan_validation_layers.rst

@@ -0,0 +1,54 @@
+.. _doc_vulkan_validation_layers:
+
+Validation layers
+=================
+
+Validation layers enable developers to verify their application's correct use
+of the Vulkan API.
+
+.. _doc_vulkan_validation_layers-android:
+
+Android
+-------
+
+After enabling validation layers on Android, a developer can see errors and
+warning messages in the ``adb logcat`` output.
+
+Enabling validation layers
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Build validation layers from official sources
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+To build Android libraries, follow the instructions on
+`Khronos' repository  <https://github.com/KhronosGroup/Vulkan-ValidationLayers/blob/master/BUILD.md#building-on-android>`__.
+After a successful build, the libraries will be located in ``Vulkan-ValidationLayers/build-android/libs``.
+
+Copy libraries
+^^^^^^^^^^^^^^
+
+Copy libraries from ``Vulkan-ValidationLayers/build-android/libs`` to
+``godot/platform/android/java/app/libs/debug/vulkan_validation_layers``.
+
+Your Godot source directory tree should look like on the example below::
+
+    godot
+    |-- platform
+        |-- android
+            |-- java
+                |-- app
+                    |-- libs
+                        |-- debug
+                            |-- vulkan_validation_layers
+                                |-- arm64-v8a
+                                |-- armeabi-v7a
+                                |-- x86
+                                |-- x86_64
+
+If the subdirectory ``libs/debug/vulkan_validation_layers`` doesn't exist, create it.
+
+Compile and run the Android app
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Linked validation layers are automatically loaded and enabled in Android debug builds.
+You can use Godot's :ref:`doc_one-click_deploy` feature to quickly test your project with the validation layers enabled.