Suggestion: Link to the Data Agent Kit extension docs

### Pre-reqs

- [x] Search the [current open issues](https://github.com/GoogleCloudPlatform/data-agent-kit/issues)

### What are you trying to do that currently feels hard or impossible?

Data Agent Kit includes an extension for VS Code and IDEs based on VS Code. This repo doesn't mention it or link to it.

### Suggested Solution(s)

You could link to the documentation from this repo's README. Pages you might consider linking to:

- Landing page: https://docs.cloud.google.com/data-cloud-extension
- Overview: https://docs.cloud.google.com/data-cloud-extension/vs-code/overview
- Install guide: https://docs.cloud.google.com/data-cloud-extension/vs-code/install

### Additional Details

_No response_