fix(docs): use double backquotes for a command

[minaminao]

📚 Description

The command sage -n jupyter was in tex format as follows.

Fixed it.

📝 Checklist

• I have made sure that the title is self-explanatory and the description concisely explains the PR.
• [ ] I have linked an issue or discussion.
• [ ] I have created tests covering the changes.
• [ ] I have updated the documentation accordingly.

⌛ Dependencies

[mezzarobba]

Other translations have the same issue:

de/tutorial/introduction.rst:-  **graphisches Notebook-Interface:** rufen Sie `sage -n jupyter` auf; lesen Sie
en/tutorial/introduction.rst:-  **Notebook graphical interface:** run ``sage -n jupyter``; see
es/tutorial/introduction.rst:-  **Interfaz gráfico del Notebook:** iniciar `sage -n jupyter`; leer
fr/tutorial/introduction.rst:-  **Interface graphique (« notebook ») :** démarrer `sage -n jupyter`; lire
ja/tutorial/introduction.rst:- **ノートブック グラフィカル インターフェイス:**  `sage -n jupyter` を起動します。pt/tutorial/introduction.rst:-  **Interface gráfica Notebook:** inicie `sage -n jupyter`; leia
ru/tutorial/introduction.rst:-  **Notebook (графический интерфейс):** запустите `sage -n jupyter`; читайте

[minaminao]

@mezzarobba fixed files in other languages

[mezzarobba]

Thanks!