Add illustrative images to documentation for enhanced clarity and visual context.

Author: gpx1000

en/Building_a_Simple_Engine/Lighting_Materials/02_lighting_models.adoc

@@ -113,6 +113,8 @@ Considerations for using PBR:
 
 For comprehensive information on PBR, see the link:https://www.pbr-book.org/[Physically Based Rendering book].
 
+image::../attachments/simple_engine/Assets/PBR_ray_shadows.png[PBR materials with ray-traced shadows - demonstrating metallic surfaces, roughness variation, and realistic shadow rendering]
+
 == Lighting Models in glTF
 
 The glTF format uses PBR with the metallic-roughness workflow, which defines materials using these primary parameters:

en/Building_a_Simple_Engine/Loading_Models/04_loading_gltf.adoc

@@ -165,6 +165,8 @@ These properties can be specified as constant values or as texture maps for
 spatial variation across the surface. We'll go into details about PBR in the
 next few chapters.
 
+image::../attachments/simple_engine/Assets/bookstand.png[Bookstand with complex PBR materials - demonstrating wood, glass, metal, and paper textures with varied material properties]
+
 ==== Texture Formats and Compression
 
 In our engine, we use KTX2 with Basis Universal compression for textures. This approach offers several advantages:

en/Building_a_Simple_Engine/introduction.adoc

@@ -54,6 +54,8 @@ xref:conclusion.adoc[Previous: Main Tutorial Conclusion] | xref:Building_a_Simpl
 
 To follow along with the attachments-based Simple Engine examples and scenes, fetch the Bistro assets locally.
 
+image::../attachments/simple_engine/Assets/MainEntry.png[The Bistro scene - a detailed outdoor café environment demonstrating the engine's rendering capabilities]
+
 - Linux/macOS (default target: attachments/simple_engine/Assets/bistro at repository root):
 +
   $ cd attachments/simple_engine