Review: jax_intro.md

Part of #40 (Phase 1).

Native-speaker review of jax_intro.md by @Honaminto.

How to reply. Open a PR editing the French directly — one PR for this lecture, titled e.g. [jax_intro] Corrections — or leave line comments / suggestion blocks on it. Priorities: meaning errors, wrong technical terms, inconsistent terminology, unnatural French (academic register), anything in code comments that looks wrong. Ignore spacing before : ; ! ?, errors in the English, and the translation: header. A wrong term that recurs belongs on the terminology issue, not here.

Done when a PR by @Honaminto touching this file is merged, or he states here that the lecture needs no change. Either outcome is recorded; nothing is ticked by hand.

Réviser lectures/jax_intro.md par rapport à la source anglaise liée, en se concentrant sur le sens, les termes techniques, la cohérence de la terminologie, le français académique et les commentaires du code. Ignorer les remarques répertoriées concernant les espacements et les en-têtes. Le travail sera terminé lorsque la PR de revue de ce fichier sera fusionnée ou que @Honaminto confirmera qu’aucune modification n’est nécessaire.