Add Tuning Engines base URI example

[cerebrixos]

Summary

• Adds a small documentation example for using Tuning Engines through the existing OpenAI-compatible configuration surface.
• Keeps the project API unchanged: no dependencies, no adapter changes, and no runtime behavior changes.
• Shows how Ruby/Rails teams can keep this project in charge of application, agent, tool, or workflow logic while routing model calls through a governed OpenAI-compatible endpoint.

Why this belongs here

Tuning Engines is an AI control plane for teams that want centralized model access, routing, tenant-scoped keys, policy/guardrail checks, audit logs, traces, approvals, and usage/cost visibility around existing AI application code.

This project already supports OpenAI-compatible configuration. The docs change makes that existing capability discoverable for Ruby/Rails teams without asking the project to add a new provider, dependency, SDK, or runtime integration.

Testing

• git diff --check

[cerebrixos]

Hello team @lancecarlson Please do consider this PR for merge. So much appreciate in advance :)