Add a "How to contribute" section in the Readme of the project

[ch33kaboo]

when I wanted to contribute I didn't know exactly how I can modify and preview my changes, and when I did the changes I didn't know how to see if the plugin is still working with the changes I made, for this, I think adding a "How to contribute" section in the Readme of the project would be helpful.
and then you can add any specific rules to contributing that you want others who would like to contribute to follow.

I can do it if you guys are comfortable with that.