Included CI/CD and security documentation

[Mehulantony]

This PR includes three key documentation files to improve project clarity, maintainability and contributor experience. The following files were created-

1. SECURITY.md - This defines proper reporting guidelines for security vulnerabilities. The document explains how contributors should report sensitive issues, what information is needed to investigate vulnerabilities, and which automated tools the project uses (Dependabot, CodeQL, npm audit), etc.
2. CHANGELOG.md - This file documents all notable changes in an organized and human-readable format. It helps contributors and maintainers to quickly understand what was added, changed or fixed. The changelog now includes CI/CD documentation and provides a strong foundation for future updates.
3. docs/ci_overview.md - Created a ci_overview.md file in the docs folder which explains the project's current CI pipeline, which includes how ESLint, Prettier, Dependabot, etc all work. This makes the CI/CD system that is implemented easier to understand and improves onboarding for new contributors. It also ensures future troubleshooting issues are handled efficiently.

[Mehulantony]

In SECURITY.md, the maintainer's name was not included; instead a placeholder is included (maintainer-name@slu.edu). Please modify this to reflect maintainer's real name if needed.