Website and docs updates

Summary:
- Added sbranson's fit mesh tutorial to the website
- Updated rendering docs with info about texturing and new shader types.

TODO:
- add pointcloud rendering tutorial to the website as well (https://github.com/facebookresearch/pytorch3d/blob/master/docs/tutorials/render_colored_points.ipynb)
- docs for camera
- update some tutorials which depended on the Textures from structures.

Reviewed By: gkioxari

Differential Revision: D23143977

fbshipit-source-id: 6843c9bf3ce11115c459c64da5b0ad778dc92177

website/sidebars.json

@@ -1,7 +1,8 @@
 {
   "docs": {
     "Introduction": ["why_pytorch3d"],
-    "Meshes": ["batching", "meshes_io"],
-    "Differentiable Renderer": ["renderer", "renderer_getting_started"]
+    "Data": ["meshes_io", "datasets", "batching"],
+    "Ops": ["cubify"],
+    "Renderer": ["renderer", "renderer_getting_started", "cameras"]
   }
 }