docs: add RenderDoc GPU debugging tools mention

docs/TROUBLESHOOTING.md

@@ -140,6 +140,14 @@ return vec4<f32>(1.0, 1.0, 1.0, 1.0);  // wrong: solid white
 - Confirm the function name in your `@vertex`/`@fragment` declaration matches the string you pass to `ProgrammableStage::entry_point`
 - If the error message is unclear, try compiling the shader in isolation to isolate syntax vs. pipeline-binding issues
 
+## 12. GPU debugging with RenderDoc
+
+**Symptom:** Rendering issues that are difficult to diagnose (artifacts, wrong output, silent failures).
+
+**Cause:** GPU debugging is hard with standard tools. Graphics pipeline state, shader execution, and buffer contents are not easily inspectable at runtime.
+
+**Fix:** Use [RenderDoc](https://renderdoc.org/) — a standalone GPU debugging tool supporting frame capture, pipeline state inspection, and shader debugging. It works with Vulkan (Linux), DX12 (Windows), and OpenGL. Launch RenderDoc, attach to your wgpu process, and capture frames to inspect the full graphics pipeline step by step.
+
 ## Additional Resources
 
 - [Glossary](concepts/GLOSSARY.md) — Every term defined