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/building_applications/index.md

@@ -1,6 +1,8 @@
 # Building AI Applications
 
-Llama Stack provides all the building blocks needed to create sophisticated AI applications. This guide will walk you through how to use these components effectively.
+[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/drive/1F2ksmkoGQPa4pzRjMOE6BXWeOxWFIW6n?usp=sharing)
+
+Llama Stack provides all the building blocks needed to create sophisticated AI applications. This guide will walk you through how to use these components effectively. Check out our Colab notebook on to follow along working examples on how you can build LLM-powered agentic applications using Llama Stack.
 
 ## Basic Inference