Set up GitHub Actions for CI

[liqingyang1606]

In order to add Continuous Integration to our project, we will need to:

• Create a .github/workflows directory in the repository
• Create a workflow.yml file and configure GitHub Actions to run test cases every time someone pushes to the master branch or submits a Pull Request
• All the while maintaining 95%+ code coverage
• Run your test cases to make sure that your tests work before creating pull requests

For more information, please check GitHub Actions page.