added contributing guidelines

CONTRIBUTING.md

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+# Contributing to Monolith
+
+Thank you for considering contributing to Monolith! Your contributions help improve this lightweight recommendation system. To ensure a smooth collaboration, please follow these guidelines.
+
+## Table of Contents
+
+- [Code of Conduct](#code-of-conduct)
+- [How Can I Contribute?](#how-can-i-contribute)
+  - [Reporting Bugs](#reporting-bugs)
+  - [Suggesting Enhancements](#suggesting-enhancements)
+  - [Submitting Pull Requests](#submitting-pull-requests)
+- [Development Setup](#development-setup)
+- [Style Guides](#style-guides)
+  - [Coding Standards](#coding-standards)
+  - [Commit Messages](#commit-messages)
+- [Community](#community)
+- [License](#license)
+
+## Code of Conduct
+
+Please note that this project is released with a [Contributor Code of Conduct](https://www.contributor-covenant.org/version/2/0/code_of_conduct/). By participating in this project, you agree to abide by its terms.
+
+## How Can I Contribute?
+
+### Reporting Bugs
+
+If you encounter a bug, please [open an issue](https://github.com/bytedance/monolith/issues) and include:
+
+- A clear and descriptive title.
+- Steps to reproduce the issue.
+- Expected and actual behavior.
+- Any relevant logs or screenshots.
+
+### Suggesting Enhancements
+
+To suggest new features or enhancements, please [open an issue](https://github.com/bytedance/monolith/issues) and provide:
+
+- A clear and descriptive title.
+- A detailed description of the proposed enhancement.
+- The motivation and use case for the enhancement.
+
+### Submitting Pull Requests
+
+Before submitting a pull request:
+
+1. Fork the repository and create your branch from `master`.
+2. Ensure your code follows the project's coding standards.
+3. Include appropriate tests for your changes.
+4. Update the documentation as needed.
+5. Verify that all tests pass.
+
+## Development Setup
+
+To set up the development environment:
+
+1. Clone the repository:
+   ```bash
+   git clone https://github.com/bytedance/monolith.git
+   ```
+2. Install [Bazel 3.1.0](https://github.com/bazelbuild/bazel/releases/tag/3.1.0) as the build tool.
+3. Build the project:
+   ```bash
+   bazel build //...
+   ```
+
+## Style Guides
+
+### Coding Standards
+
+- Follow the existing code style in the repository.
+- Write clear and concise code with appropriate comments.
+
+### Commit Messages
+
+- Use the present tense ("Add feature" not "Added feature").
+- Keep messages brief and descriptive.
+- Reference issues and pull requests when applicable.
+
+## Community
+
+Join our community discussions on [Discord](https://discord.gg/QYTDeKxGMX) to connect with other contributors and maintainers.
+
+## License
+
+By contributing, you agree that your contributions will be licensed under the [Apache 2.0 License](https://github.com/bytedance/monolith/blob/master/LICENSE).
+
+---
+
+Thank you for your contributions!