Update intro.md [Doc French translation]

[beryl-dlg]

Motivation for the change, related issues

Hello, following the path to inaugurate french translations to the Playground documentation
Initiated with @jennydupuy at the last WordCamp Bretagne Contribution Day 2025

Sorry if I didn't do it right, I'm not sure I should have made a PR but i'm not familiar with this process…

https://wordpress.github.io/wordpress-playground/contributing/translations/

Implementation details

Testing Instructions (or ideally a Blueprint)

[adamziel]

Thank you so much! It seems like there's one flaky failing CI check that we can ignore, and one actual issue reported by the runner — it detected a dead link. I'm on my phone and not sure if that's accurate — let me loop in @juanmaguitar who initially set up the language support

[juanmaguitar]

Thanks for this work @beryl-dlg. I have added a few comments.

Once you have applied these changes you can test them locally by going to /wordpress-playground/packages/docs/site and from that folder run

npm run dev -- --locale fr

PS: The command above requires that previously the dependencies of the project had been installed by doing npm install from /wordpress-playground