Request: Add Contribution Guide

[sntomo]

I am new to contributing to open source, and while I was setting up the development environment to contribute to Chronos, I noticed that there doesn’t seem to be a Contribution Guide available, unlike in the main CakePHP repository.

Specifically, I couldn't find any documentation on how to run tests or other development practices, and it seems that some things are left as implicit knowledge.

To make it easier for OSS beginners like myself to contribute to the project, would you consider adding a Contribution Guide?

Thank you for considering this suggestion. I appreciate your time and effort in improving the project!

[dereuromark]

Do you want to make a PR and add the necessary info?