Fix deprecated OpenAI v0 API and add requirements.txt

[rafaym1]

What

run_bfi.py and run_creative_writing.py use openai.ChatCompletion.create() which was removed in openai>=1.0.0 (Nov 2023). Anyone installing the package today gets v1.x and hits an AttributeError immediately.

Also adds a missing requirements.txt and updates the README setup instructions (the referenced audiencenlp conda environment was not included in the repo).

Changes

• run_bfi.py / run_creative_writing.py: migrate to openai>=1.0.0 client API
  • import openai → from openai import OpenAI
  • removed hardcoded empty openai.api_key = "" / openai.organization = ""
  • openai.ChatCompletion.create() → client.chat.completions.create()
  • response access: response["choices"][0]["message"]["content"] → response.choices[0].message.content
  • API key now read from OPENAI_API_KEY environment variable
• requirements.txt: added (was missing entirely)
• README.md: replaced conda activate audiencenlp with pip install -r requirements.txt and env var setup instructions