Recommend triangulating and applying transforms in Importing 3D scenes (#4742)

This is generally good advice for any 3D engine, but Godot also has
issues with 3D selection that are more present with misaligned objects.

getting_started/workflow/assets/importing_scenes.rst

@@ -13,10 +13,10 @@ transferred as close as possible.
 
 Godot supports the following 3D *scene file formats*:
 
-* glTF 2.0. Godot has full support for text and binary formats.
+* glTF 2.0 **(recommended)**. Godot has full support for both text (``.gltf``) and binary (``.glb``) formats.
 * DAE (COLLADA), an older format that is fully supported.
-* OBJ (Wavefront) formats. It is also fully supported, but pretty limited (no support for pivots, skeletons, etc).
-* ESCN, a Godot specific format that Blender can export with a plugin.
+* OBJ (Wavefront) format + their MTL material files. This is also fully supported, but pretty limited (no support for pivots, skeletons, animations, PBR materials, ...).
+* ESCN, a Godot-specific format that Blender can export with a plugin.
 * FBX, supported via the Open Asset Import library. However, FBX is proprietary, so we recommend using other formats
   listed above, if suitable for your workflow.
 
@@ -79,6 +79,36 @@ experimental.
 The ESCN exporter has a detailed `document <escn_exporter/index.html>`__ describing
 its functionality and usage.
 
+Exporting textures separately
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+While textures can be exported with a model in certain file formats, such as glTF 2.0, you can also export them
+separately. Godot uses PBR (physically based rendering) for its materials, so if a texturing program can export PBR
+textures, they can work in Godot. This includes the `Substance suite <https://www.substance3d.com/>`__,
+`ArmorPaint (open source) <https://armorpaint.org/>`__, and `Material Maker (open source) <https://github.com/RodZill4/material-maker>`__.
+
+.. note:: For more information on Godot's materials, see :ref:`doc_spatial_material`.
+
+Exporting considerations
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Since GPUs can only render triangles, meshes that contain quads or N-gons have
+to be *triangulated* before they can be rendered. Godot can triangulate meshes
+on import, but results may be unpredictable or incorrect, especially with
+N-gons. Regardless of the target application, triangulating *before* exporting
+the scene will lead to more consistent results and should be done whenever
+possible.
+
+To avoid issues with incorrect triangulation after importing in Godot, it is
+recommended to make the 3D DCC triangulate objects on its own. In Blender, this
+can be done by adding a Triangulate modifier to your objects and making sure
+**Apply Modifiers** is checked in the export dialog. Alternatively, depending on
+the exporter, you may be able to find and enable a **Triangulate Faces** option
+in the export dialog.
+
+To avoid issues with 3D selection in the editor, it is recommended to apply the
+object transform in the 3D DCC before exporting the scene.
+
 Import workflows
 ----------------