Minor Markdown improvements on packaging page

[santisoler]

Apply some minor improvements to the Markdown syntax in the pages instruction on how to create the pyproject.toml file.

This PR was created during SciPy2024 sprints.

TODO

• [ ] wait for #340 to be merged and update this branch
• [ ] update the Spanish translation of modified lines
• [ ] locally build the translated pages to check they work properly