add: segmentation guide.
_The documentation is not available anymore as the PR was closed or merged._ Thanks @osanseviero. Am I good to merge?  I would wait for a second approval just in case :)  Sure :)  Merging since the images have been pushed as LFS files ([PR](https://huggingface.co/datasets/huggingface/documentation-images/discussions/8)). 
Closes #5181 

I have opened a PR on Hub (https://huggingface.co/datasets/huggingface/documentation-images/discussions/5) to include the images in our central Hub repository. Once the PR is merged I will edit the image links. 

I have also prepared a [Colab Notebook](https://colab.research.google.com/drive/1BMDCfOTBnyshoME5RSxn5iQy-TWeFbOA?usp=sharing) in case anyone wants to play. 

- [x] Replace the image links 