Introduce contribution guidelines

[qurbonzoda]

The current README.md references a non-existent document for contribution guidelines. To address this, we need to create a comprehensive document on contribution guidelines inspired by the best practices observed in contribution guidelines of other kotlinx libraries.

This document should cover, but not be limited to:

• How to set up the development environment
• Step-by-step instructions for submitting contributions
• Code style and conventions to follow
• A detailed section on how to build the project, including any prerequisites and common troubleshooting steps.