[DOC] Document nvdashboard jupyterlab toggle accelerator for cudf.pandas

## Documentation proposal

Since the jupyterlab-nvdashboard 0.15 release extension, if a user has cudf installed, the GPU toggle for cudf.pandas will be enabled. xref PR: https://github.com/rapidsai/jupyterlab-nvdashboard/pull/248

This page https://docs.nvidia.com/cudf/26.08/cudf_pandas/usage/ should include documentation on how to use this feature.

For reference this is a short video explaining how it works. https://github.com/rapidsai/jupyterlab-nvdashboard/pull/248#issuecomment-3955417685

We could limite this to a few screenshots, for simplicity since the video is long.

**Suggested fix for documentation**

I can make this contribution, I'd like a minimal guidance on the preferred way to contribute this.

Do you prefer screenshots, or a shorter video/gif ?