Create CONTRIBUTING.md to help open source devs onboard

[PaddyMc]

Create a CONTRIBUTING.md file, It will help attract open-source devs and also give people a good idea of our values.

Reasoning Example

[mohoff]

great! @PaddyMc wanna pick it up?

[PaddyMc]

Would love to @mohoff , but unfortunately, I don't have the availability to complete this task atm.