website and README updates

Summary: Small updates to the website setup before the website is updated

Reviewed By: bottler

Differential Revision: D24880351

fbshipit-source-id: 5c40664ad1ca3dd9f4fc746b239a82d47ed3a8e6

website/sidebars.json

@@ -3,6 +3,7 @@
     "Introduction": ["why_pytorch3d"],
     "Data": ["meshes_io", "datasets", "batching"],
     "Ops": ["cubify"],
+    "Visualization": ["visualization"],
     "Renderer": ["renderer", "renderer_getting_started", "cameras"]
   }
 }