What does this PR do?

Improve repo

IMPORTANT

• Read our contributing guidelines.
• This is not a revision of a previous PR.

For resources

Description

This PR updates the Spanish contributor guide (CONTRIBUTING-es.md) to improve grammar, consistency, and readability.

Why is this valuable (or not)?

This helps maintain translation quality and accessibility for Spanish-speaking contributors, ensuring the documentation is current, accurate, and easier to follow.

How do we know it's really free?

N/A — this PR modifies documentation, not external resources.

For book lists, is it a book? For course lists, is it a course? etc.

N/A — documentation file, not a list entry.

Checklist:

• Searched for duplicates (not applicable).
• Included proper Markdown formatting and consistent structure.
• Preserved alphabetical and spacing conventions where relevant.
• Used an informative name for this pull request.

Follow-up

I will monitor GitHub Actions and address any reported warnings or formatting issues.

Reviewed and updated by @FelipeChicaiza