Improve GDExtension tutorial based on own experience

Clarified that there is a difference from _process in GDScript.
Changed the wording around SConstruct file to make it less intimidating.
Added some hints about things that can be done with SCons to improve UX.

Author: Maarrk

tutorials/scripting/gdextension/gdextension_cpp_example.rst

@@ -212,6 +212,12 @@ call to find out which methods can be called and which properties it exposes.
 The second is our ``_process`` function, which will work exactly the same
 as the ``_process`` function you're used to in GDScript.
 
+.. note::
+
+    Unlike GDScript, the GDExtension ``_process`` will be run as soon as it is
+    loaded, not only in game. See also :doc:`Running code in the editor <../../plugins/running_code_in_the_editor>`
+    for more information on how to handle that.
+
 Let's implement our functions by creating our ``gdexample.cpp`` file:
 
 .. code-block:: cpp
@@ -327,10 +333,11 @@ At last, we need the header file for the ``register_types.cpp`` named
 Compiling the plugin
 --------------------
 
-We cannot easily write by hand a ``SConstruct`` file that SCons would use for
-building. For the purpose of this example, just use
-:download:`this hardcoded SConstruct file <files/cpp_example/SConstruct>` we've
-prepared. We'll cover a more customizable, detailed example on how to use these
+To compile the project we need to define it for SCons using another
+``SConstruct`` file which references the one in ``godot-cpp``.
+Writing it from scratch is outside the scope of this tutorial, but you can
+:download:`the SConstruct file we prepared <files/cpp_example/SConstruct>`.
+We'll cover a more customizable, detailed example on how to use these
 build files in a subsequent tutorial.
 
 .. note::
@@ -711,6 +718,22 @@ Every second, we output our position to the console.
 Next steps
 ----------
 
-We hope the above example showed you the basics. You can
-build upon this example to create full-fledged scripts to control nodes in Godot
-using C++.
+We hope the above example showed you the basics. You can build upon this
+example to create full-fledged scripts to control nodes in Godot using C++.
+
+If you want to include other C++ libraries, consider using submodules for
+getting them into your project, in the same way as we did with ``godot-cpp``.
+Then you will need to add them to the ``SConstruct`` file. For details, consult
+the `SCons documentation <https://scons.org/documentation.html>`__, but it may
+require as little as adding these lines to the file:
+
+.. code:: python
+
+    env.Append(CPPPATH=["library-path/src/", "library-path/include/"])
+    sources = sources + Glob("library-path/src/*.cpp")
+
+If your editor is using `clangd Language Server <https://clangd.llvm.org/>`__
+to provide smart C++ features, but it doesn't know where to find the headers,
+you can fix that by `generating compile_commands.json with Scons <https://scons.org/doc/latest/HTML/scons-user/ch27.html>`__.
+This should enable actions like "go to definition", also for ``godot-cpp``
+functions and types.