GitLab

* Rename index.mdx to index.md

* With saved modifs

* Address review comment

* Treat all files

* .mdx -> .md

* Remove special char

* Update utils/tests_fetcher.py
Co-authored-by: Lysandre Debut <lysandre.debut@reseau.eseo.fr>

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Co-authored-by: Lysandre Debut <lysandre.debut@reseau.eseo.fr>

Left the term fine-tuning since there is no correct translation into Italian and the English term is generally used. The same was done with some terms like "learning rate"

* added training.mdx

* updated training.mdx

* updated training.mdx

* updated training.mdx

* updated _toctree.yml

* fixed typos after review
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>