Update ToC

Author: aleino-nv

docs/user-guide/toc.html

@@ -135,6 +135,7 @@
 <li data-link="targets#metal"><span>Metal</span></li>
 <li data-link="targets#cuda-and-optix"><span>CUDA and OptiX</span></li>
 <li data-link="targets#cpu-compute"><span>CPU Compute</span></li>
+<li data-link="targets#webgpu"><span>WebGPU</span></li>
 <li data-link="targets#summary"><span>Summary</span></li>
 </ul>
 </li>