Add info to turn off preview sunlight before working with 3D shader lighting.

By default in Godot 4.3, preview sunlight is enabled and only disabled by a DirectionalLight3D being added to the scene. If you follow the guide and add an OmniLight3D, the preview sunlight stays enabled and causes a drastically different look.

Author: FarzadBT

tutorials/shaders/your_first_shader/your_first_3d_shader.rst

@@ -277,6 +277,7 @@ Interacting with light
 
 First, turn wireframe off. To do so, click in the upper-left of the Viewport
 again, where it says "Perspective", and select "Display Normal".
+Additionally in the 3D scene toolbar, toggle off preview sunlight.
 
 .. image:: img/normal.png