Add a gradio demo for the python sdk section

[yvrjsharma]

Hello there! I would like to request a new sub-section for a Gradio demo that can be added under the Python SDK section in your readme file. Gradio's ChatInterface tool is a great way to quickly create batch or streaming chat demos. You can find a helpful guide to using it on our docs website. If you encounter any issues along the way, the Gradio team is always here to help.