Add contribution guidelines

[vpanyushenko]

We need to determine what is needed for someone to add to the UI Kit. Some questions to consider:

• Why are certain components added vs rejected?
• What is the process of adding a component?
• Do we need to add designs first?
• Does the component need to follow a specific convention?

[vpanyushenko]

We can make the repo public after we add these prelim docs.

[clearly-outsane]

That makes sense. Is there something I could reference for what Bubble's opinion might be to base decisions off of? Like for example sometimes I'm not sure if I show put all the features into the component itself ( so its abstracted from the end user) or instead just provide ways for it to be integrated with whatever approach the end user wants. (since it's easy to do certains things in svelte but need third party tooling in react)