Update Overview.ipynb google colab
_The documentation is not available anymore as the PR was closed or merged._ WDYT @albertvillanova ? The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_5211). All of your documentation changes will be reflected on that endpoint.
- removed metrics stuff
- added image example
- added audio example (with ffmpeg instructions)
- updated the "add a new dataset" section