add colab notebook & update docs (#619)

# What does this PR do?

- add notebooks
- restructure docs

## Test Plan
<img width="1201" alt="image"
src="https://github.com/user-attachments/assets/3f9a09d9-b5ec-406c-b44b-e896e340d209"
/>

<img width="1202" alt="image"
src="https://github.com/user-attachments/assets/fdc1173f-2417-4ad6-845e-4f265fc40a31"
/>

<img width="1201" alt="image"
src="https://github.com/user-attachments/assets/b1e4e2a8-acf6-4ef2-a2fc-00d26cf32359"
/>


## Sources

Please link relevant resources if necessary.


## 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](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Updated relevant documentation.
- [ ] Wrote necessary unit or integration tests.

docs/source/concepts/index.md

@@ -62,3 +62,13 @@ While there is a lot of flexibility to mix-and-match providers, often users will
 
 
 **On-device Distro**: Finally, you may want to run Llama Stack directly on an edge device (mobile phone or a tablet.) We provide Distros for iOS and Android (coming soon.)
+
+## More Concepts
+- [Evaluation Concepts](evaluation_concepts.md)
+
+```{toctree}
+:maxdepth: 1
+:hidden:
+
+evaluation_concepts
+```