Add colab/jupyter notebook in getting started page (#3885)

Summary:
Pull Request resolved: #3885

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Oncall Short Name: executorch

Reviewed By: mcr229, cccclai

Differential Revision: D58262970

fbshipit-source-id: 0777670706e4a949ffd2bf9e82b77d968f39ee1a

docs/source/getting-started-setup.md

@@ -68,6 +68,12 @@ Note that the cross-compilable core runtime code supports a wider range of
 toolchains, down to C++11. See the [Runtime Overview](./runtime-overview.md) for
 portability details.
 
+## Quick Setup: Colab/Jupyter Notebook Prototype
+
+To utilize ExecuTorch to its fullest extent, please follow the setup instructions provided below. Alternatively, if you would like to experiment with ExecuTorch quickly and easily, we recommend using the following [colab notebook](https://colab.research.google.com/drive/1qpxrXC3YdJQzly3mRg-4ayYiOjC6rue3?usp=sharing) for prototyping purposes.
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 ## Environment Setup
 
 ### Create a Virtual Environment