Set up Read the Docs hosting for this repo

The repo already contains all the in-tree docs infrastructure:

• .readthedocs.yml, docs/conf.py, docs/index.rst, docs/instrumentation/*.rst
• rtd-requirements.txt / docs-requirements.txt
• A CI docs job (tox -e docs) that builds the docs on every PR

What's missing is the Read the Docs project itself. https://opentelemetry-python-genai.readthedocs.io/ currently returns 404 — no RTD project is registered for this repo, so docs are never published.

This requires an action by someone with OpenTelemetry org admin access (outside the repo):

1. Create a Read the Docs project for open-telemetry/opentelemetry-python-genai (matching the existing slug opentelemetry-python-genai so existing links resolve).
2. Connect the GitHub webhook so pushes to main and tags trigger builds.
3. Verify the build succeeds and latest resolves.

Review .readthedocs.yml, docs/conf.py, docs/index.rst, and the existing tox -e docs CI job first. An OpenTelemetry organization admin must register the matching Read the Docs project, connect the GitHub webhook, and verify that the build succeeds and the latest URL resolves.