docs: Add organization-wide CONTRIBUTING.md file

[GuDevBot]

What this PR does

This Pull Request introduces a CONTRIBUTING.md file to the root of the .github repository.

This file will serve as the default contribution guide for all current and future projects under the AlphaRages organization, establishing a clear and standard process for community contributions.

Why this change is important

The current README.md file directs potential contributors to reach out via email or other contact channels. This can be a barrier to entry and is not a standard practice in open-source communities.

By adding a dedicated CONTRIBUTING.md file, we:

• Lower the barrier for new contributors.
• Align the organization with open-source best practices.
• Provide a clear, step-by-step workflow for reporting bugs, suggesting features, and submitting code.
• Create a more welcoming and professional environment for the community.

This change helps fulfill the "Open Source Philosophy" mentioned in the organization's profile, making it easier for developers to collaborate and contribute effectively.

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For Maintainers: Next Steps

To complete this setup, the following action is recommended:

• Update the Code of Conduct Link: The CONTRIBUTING.md file currently has a placeholder link for the Code of Conduct. It is recommended to create a CODE_OF_CONDUCT.md file within this .github repository. Once created, the link in the CONTRIBUTING.md file should be updated to point to it.