Add contributors and edit guideline and metadata for paper submission

[ZarrinGEM]

This PR includes several updates for the paper submission:

✅ Contribution Guidelines

• Added basic instructions for users unfamiliar with git.
• Fault Plane Generation Documentation (Wells and Coppersmith 1994). Included relevant scripts in the src folder.
• Added a section listing the minimum expected impact metrics (e.g., fatalities, injured, displaced) in the contribution guidelines to guide future data submissions.

✅ Metadata Update

• Explained that empty cells in the dataset do not indicate zero impact, but rather missing or unavailable data, to avoid misinterpretation.

✅ Contributors Acknowledgment

• Added contributors’ names (e.g., Luis Mixco for the 2001 El Salvador events, SURA, Sevgi and Santiago) to the main README of each event folder.

[CatalinaYepes]

To adjust:

• Include Maria Camila in the Contributors section.
• For El Salvador, include Manuel Lopez from UES (University of El Salvador).
• Rename the file test.py. It should reflect the purpose of the script (it's not a test). For example, example_build_rupture.py

[ZarrinGEM]

To adjust:

* Include Maria Camila in the `Contributors` section.

* For El Salvador, include Manuel Lopez from UES (University of El Salvador).

* Rename the file `test.py`. It should reflect the purpose of the script (it's not a test). For example, `example_build_rupture.py`

@CatalinaYepes I've made the requested changes. Please take a look and accept the PR when you get the chance. Thanks!

[CatalinaYepes]

LGTM