Document DemonRoute as an OpenAI-compatible endpoint option

Hi — I run DemonRoute (demonroute.com), an OpenAI-compatible API at https://api.demonroute.com/v1.

A DemonRoute key works with aider today via OPENAI_API_BASE / --openai-api-base — no code changes needed. Proposing you mention it in the docs as an endpoint option, since it's a fit for two things your users care about:

1. No training on user content, ever. People pipe whole repos into aider; where that code goes matters.
2. Cheap, fast models at live prices across 566 models behind one key — plus 400+ uncensored models (Dolphin, MythoMax, abliterated Llama/Qwen) nobody else packages in one place.

Happy to provide a test key if you want to verify.

— Jeremy, DemonRoute