Add AI Badgr as optional OpenAI-compatible backend

[michaelmanly]

This PR adds documentation for using AI Badgr as an optional OpenAI-compatible backend.

What’s changed

• Adds a short docs section explaining how to point existing OpenAI-style config to AI Badgr
• Shows how to set:
  • base_url = https://aibadgr.com/api/v1
  • api_key = AI Badgr API key
• Includes minimal examples (Python / JavaScript / cURL)

Notes

• Docs-only change – no code or behavior changes
• Optional provider – nothing in the project depends on AI Badgr
• Follows the same pattern as other provider docs in this repo

Contributor License Agreement: I agree to the contributor license agreement terms for this repository.

[michaelmanly]

xtekky/gpt4free#3284 (comment)