Add new article-to-podcast cookbook

[yiren-openai]

• Add new cookbook (similar to NotebookLM feature) that converts a text article to a short podcast episode
• The motivation here is to give newsrooms an example of the sort of new reader experiences that are possible with OpenAI

[glojain]

Adding comments here since I can't comment on the python notebook diff directly:
Step 2:
The script is intended to be under 5 minutes, but in multiple tests, the voice output is consistently around 6–7 minutes. I'd consider testing out how to best get to that 5 minute length in Step 4.

Step 3:
I would clarify what users should sanity check for here.

Step 4:
I'd recommend adding https://openai.fm/ so users can easily explore the different voice configurations.

“You’re done” section:
nit: Instead of saying “OpenAI helps lower the barrier” (which might feel a bit too promotional for the Cookbook), I'd add: “Our text-to-speech models make it easier to experiment with audio storytelling […]”

Next steps section:
I’d recommend adding a “Next Steps” section to encourage further exploration: using the Realtime API to chat with the article, or adding support for multiple input formats like non-Markdown files.