add: folder for notebooks

[GHCamille]

No description provided.

[frgfm]

Thanks for the PR!
A few suggestions:

• why not adding directly non empty notebooks?
• let's name the files without spaces (underscores as replacement for instance)
• to avoid too much "content" files in the repo, I might suggest an alternative: only having a markdown file with links to the notebook + colab options, and we create another repo that will hold all the notebooks for pyronear projects. I did it for a personal project: https://github.com/frgfm/torch-cam/tree/main/notebooks (and the notebooks are actually hosted here https://github.com/frgfm/notebooks/tree/main/torch-cam)

What do you think?