add pandas to env command
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_3871). All of your documentation changes will be reflected on that endpoint. Think failures are unrelated - feel free to merge whenever you want :-)
Pandas is a required packages and used quite a bit. I don't see any downside with adding its version to the `datasets-cli env` command.