docs: improve codex review for github integration

What issue are you seeing?

I have codex integrated with my github and I ask it for reviews. I notice that I always only get one comment.

I found two methods to integrate it:

1. via ci: https://github.com/openai/openai-cookbook/blob/main/examples/codex/build_code_review_with_codex_sdk.md
2. via comment directly in github mentioning (@codex): https://developers.openai.com/codex/integrations/github/

Now the latter document doesn't specify at all what P0 or P1 is and therefore how to improve the reviews via the AGENTS.md.

I am also not sure whether the first link is still the recommended way of using codex in github for PR reviews.

Please tell me how openai uses codex as reviewer and how to give it direction / context.

What steps can reproduce the bug?

Search for how to integrate codex and how to improve it, no clear one way of doing it.

What is the expected behavior?

A way to improve / change the way codex does reviews.

Additional information

_No response_