Add a: "How to run tests" Section to the README.md file

[dxL1nus]

Please add a "How to run tests" Section to the README.md file

Depends on #4

• if there is more than one step to running tests, then: Maybe create a guide on how to run tests somewhat similar to the contribution guidelines (view: https://github.com/codecheckers/ojs-codecheck/blob/main/CONTRIBUTING.md)
• mention command to run tests in this section

[dxL1nus]

@Subhanaliweb I have assigned you for this issue, as I hope that you know how to run the tests