Add arch diagram + more info about gdb debugging

reference/introduction_to_godot_development.rst

@@ -3,14 +3,38 @@
 Introduction to Godot development
 =================================
 
-This page introduces the global organization of Godot Engine's source
-code.
+This page is maent to introduce the global organization of Godot Engine's
+source code, and give useful tips for extending/fixing the engine on the
+C++ side.
+
+Architecture diagram
+--------------------
+
+The follow diagram describes the architecture used by Godot, from the
+core components down to the abstracted drivers drivers, via the scene
+structure and the servers.
+
+.. image:: /img/architecture_diagram.jpg
 
 Debugging the editor with gdb
 -----------------------------
 
-If you are writing or correcting bugs affecting Godot Engine editor,
-remember that the binary runs the launcher first, which runs the editor
-in another process. Thus, you need to run the editor directly by passing
-the ``-e`` argument to Godot Engine editor's binary from within your
-project's folder.
+If you are writing or correcting bugs affecting Godot Engine's editor,
+remember that the binary will by default run the project manager first,
+and then only run the editor in another process once you've selected a
+project. To launch a project directly, you need to run the editor by
+passing the ``-e`` argument to Godot Engine's binary from within your
+project's folder. Typically:
+
+.. code:: bash
+
+    $ cd ~/myproject
+    $ gdb godot
+    > run -e
+
+Or:
+
+.. code:: bash
+
+    $ gdb godot
+    > run -e -path ~/myproject