Update Cerebras docs to include header

[henrytwo]

What does this PR do?

I noticed that the documentation for other providers have this header, so I have added it to the Cerebras docs too.

---
orphan: true
---

# TGI Distribution

```{toctree}
:maxdepth: 2
:hidden:

self
    ```

This also fixes a typo in README.md where the link to the Cerebras docs included an extra getting_started section.

I did notice however that https://hub.docker.com/r/llamastack/distribution-cerebras still does not exist. How do I get the Cerebras Docker image uploaded?

cc: @ashwinb @raghotham

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Ran pre-commit to handle lint / formatting issues.
• Read the contributor guideline,
  Pull Request section?
• Updated relevant documentation.
• Wrote necessary unit or integration tests.