[Suggestion] Clarify support for both R and Python in README and extension webpage

[grivasgervilla]

First of all, thank you for this extension! It is incredibly useful for the community.

I’ve noticed that the current README.md and the extension's webpage primarily mention the shinylive-python option. Because of this, users might get the impression that only Shiny apps written in Python can be embedded in Quarto documents using this extension.

To prevent confusion and improve discoverability for R users, I suggest updating the documentation to explicitly state that both R and Python Shiny apps are supported.