Add: overview about .citation.cff files on GitHub

[lwasser]

This issue involves writing new text about this file in our guidebook. It is beginner friendly in that you could complete this totally on the github GUI or even in a hackmd document and we can help you with the PR if you aren't a github user!

Add information about the citation.cff file to the license page:

• how .cff files work - what they add to the repo
• how dates are tracked in this file
• how they integrate into / with zenodo

[SanketKumarKar]

What is a CITATION.cff file?
A CITATION.cff file is a simple, human- and machine-readable file (written in YAML format) that you add to the root of your repository. Its main purpose is to tell others how to cite your software correctly. When you include a CITATION.cff file, GitHub will automatically show a “Cite this repository” button, making it easy for users to find the citation information.

What does a CITATION.cff file add to your repository?
Citation Instructions: It provides clear instructions on how to cite your work.
Metadata: It contains important metadata about your project, such as authors, title, version, and more.
Machine Readability: Citation tools and services (like GitHub and Zenodo) can read this file to generate standardized citation formats automatically.
How are dates tracked in CITATION.cff?
The CITATION.cff file can include fields such as date-released (and optionally, date-created and date-modified). These dates help others know when your code was published, and they are included in citations generated from the file.

Example:

YAML
date-released: "2024-06-01"
How does CITATION.cff integrate with Zenodo?
Zenodo is a popular service for archiving research outputs and assigning DOIs (Digital Object Identifiers). When you connect your GitHub repository to Zenodo, Zenodo reads the CITATION.cff file (if present) and uses the metadata to create accurate citations for each version it archives. This ensures consistency and saves you time, as you only need to maintain your citation info in one place.

In summary:
Adding a CITATION.cff file to your repository helps others cite your work properly, tracks important dates, and ensures your citations are up-to-date and consistent across platforms like GitHub and Zenodo.

[lwasser]

@all-contributors please add @SanketKumarKar for code