Add basic contribution file

Author: ethanshar

CONTRIBUTING.md

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+# Contributing
+If you got here it means you want to dedicate some of your time and help us with making this library better.  
+So first, thank you ❤️
+
+When contributing to this repository, please first discuss the change you wish to make via [issue](https://github.com/wix/react-native-ui-lib/issues/new/choose),
+[Discord channel](https://discord.gg/2eW4g6Z), or any other method with the owners of this repository before making a change. 
+
+## Pull Request Process
+
+1. First make sure the environment is working and synced with master. For installation details go [here](https://github.com/wix/react-native-ui-lib/blob/master/markdowns/getting-started/setup.md#demo-app)
+2. Before submitting a PR we suggest running `npm run prepush` command that verifies lint, TS and tests were not broken.
+3. Please don't change our PR template.
+- 3.1 In descripton add everything that can help the reviewer and ease the reviewing process. 
+- 3.2 In the changelog it's importatnt a message for the library users - this message will be included in our release notes
+4. We try to make the PR review process as quick as possible, please be patient
+
+
+
+### Code Standards
+
+- Readability and clean code above all - we believe a clean code is easier to maintain and refactor when needed. 
+- Deciding on an API is not trivial but we always aim to keep it generic and clear - feel free to consult with us.
+- Our documentation is derived from our components' prop comments, make sure to add a clear description when adding new props. 
+- When possible, consider adding tets for a new functionality you add.
+- 
+
+
+## Typescript Status
+Currently most of our code is migrated to typescript though we still have some leftovers of javascript code and manual typings.  
+Till we complete the migration you require to do the following for new TS files
+
+Before pushing new code make sure to run `npm run build:dev` - this check for TS errors and create appropriate declarations (`d.ts`) files under generatedTypes folder. Make sure to push these files as well!