docs: move shader troubleshooting from renderfusion to arena-unity

The WorkflowMode / glTFast shader variant issue is an arena-unity
concern (glTFast is its dependency), not specific to RenderFusion.

Author: mwfarb

README.md

@@ -54,17 +54,6 @@ If you see `Subscribed FAILED to: realm/s/<ns>/<scene>/r/+/+/-/#` in the Unity c
 
 The warning `Scene remote rendering changes for topic type 'r' only available to Google authenticated scene Owner and Editors by API request` means your publish permissions do not cover the render topic. The same ownership/editor requirements apply as above.
 
-### Shader errors (`_WorkflowMode` or pink/magenta materials)
-
-If you see errors about missing shader properties like `_WorkflowMode`, or GLTF models render as pink/magenta, this is typically a **glTFast shader variant stripping issue**. Unity's build pipeline strips shader variants it considers unused, but glTFast needs them at runtime for glTF import.
-
-To fix:
-1. Go to **Edit > Project Settings > Graphics**
-2. Under **Shader Preloading**, add the glTFast shaders (`glTF/PbrMetallicRoughness`, `glTF/PbrSpecularGlossiness`, `glTF/Unlit`) to the **Always Included Shaders** list
-3. Alternatively, create a `ShaderVariantCollection` that includes the required variants
-
-If the error specifically mentions `_WorkflowMode`, your URP version may not match what glTFast expects. Ensure your URP package is compatible with your glTFast version.
-
 ## Alternate Server Usage
 
 In addition to the above, you may deploy your own ARENA webserver if you do not wish to use our test deployment server at [arenaxr.org](https://arenaxr.org). You can follow our setup guidelines in [arenaxr/arena-services-docker](https://github.com/arenaxr/arena-services-docker), to run your own server.