[ONNX] Add and fix custom cards for ONNX (#3287)

* add and fix custom cards for ONNX

Author: titaiwangms

index.rst

@@ -265,10 +265,17 @@ Welcome to PyTorch Tutorials
    :tags: Production,ONNX,Backends
 
 .. customcarditem::
-   :header: Introduction to ONNX Registry
-   :card_description: Demonstrate end-to-end how to address unsupported operators by using ONNX Registry.
+   :header: Extending the ONNX exporter operator support
+   :card_description: Demonstrate end-to-end how to address unsupported operators in ONNX.
    :image: _static/img/thumbnails/cropped/Exporting-PyTorch-Models-to-ONNX-Graphs.png
-   :link: advanced/onnx_registry_tutorial.html
+   :link: beginner/onnx/onnx_registry_tutorial.html
+   :tags: Production,ONNX,Backends
+
+.. customcarditem::
+   :header: Exporting a model with control flow to ONNX
+   :card_description: Demonstrate how to handle control flow logic while exporting a PyTorch model to ONNX.
+   :image: _static/img/thumbnails/cropped/Exporting-PyTorch-Models-to-ONNX-Graphs.png
+   :link: beginner/onnx/export_control_flow_model_to_onnx_tutorial.html
    :tags: Production,ONNX,Backends
 
 .. Reinforcement Learning