[Doc] CONTRIBUTING.md Guidelines

[dudash]

Is your asset request related to a problem? Please describe. Yes, folks new to the project need some guidelines on how to contribute

Is this a new asset or a modification/increment to an existent asset? New asset

Describe alternatives you've considered None

Additional context Typical of github projects to name this CONTRIBUTING.md For example: https://github.com/godotengine/godot/blob/master/CONTRIBUTING.md