fr: add translation for How to write in Markdown (#19876)

* translated files/en-US/mdn/writing_guidelines/howto/markdown_in_mdn/index.md in French

* Update files/fr/mdn/writing_guidelines/howto/markdown_in_mdn/index.md

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* Update files/fr/mdn/writing_guidelines/howto/markdown_in_mdn/index.md

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* Update files/fr/mdn/writing_guidelines/howto/markdown_in_mdn/index.md

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* Update files/fr/mdn/writing_guidelines/howto/markdown_in_mdn/index.md

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* Update files/fr/mdn/writing_guidelines/howto/markdown_in_mdn/index.md

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* Update files/fr/mdn/writing_guidelines/howto/markdown_in_mdn/index.md

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* Update files/fr/mdn/writing_guidelines/howto/markdown_in_mdn/index.md

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* Update files/fr/mdn/writing_guidelines/howto/markdown_in_mdn/index.md

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* lint: Lint text, code, macros and wordings (pass one)

* lint: typo, wordings, inclusivity (pass two)

* lint: linter changes following typo fix

* fix: disable example lint check

* Rewording / fixes

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