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CONTRIBUTING.md

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+# How to contribute
+
+Thanks for considering to contribute this project. All issues and pull requests are highly appreciated.
+
+## Report Issue
+
+Reporting an [issue](https://github.com/didi/rdebug/issues) is welcomed. But do please include the following details
+
+1. Environment (OS version, rdebug version and so on)
+2. Issue description, error logs
+3. Steps to reproduce
+
+## Pull Requests
+
+Before sending pull request to this project, please read and follow guidelines below.
+
+1. Coding style: PHP follow PSR-2 coding style.
+3. Commit message: Use English and be aware of your spell.
+4. Test: Make sure to test your code.
+
+NOTE: We assume all your contribution can be licensed under the [Apache License 2.0](./LICENSE).
+
+## Run Tests
+
+To run tests simply run the `phpunit` executable in the `vendor/bin`
+
+```bash
+$ composer install --dev
+$ ./vendor/bin/phpunit
+```
+
+You should get an output similar to this:
+
+```bash
+$ ./vendor/bin/phpunit
+PHPUnit 6.5.14 by Sebastian Bergmann and contributors.
+
+.................SS                                               19 / 19 (100%)
+
+Time: 152 ms, Memory: 6.00MB
+
+OK, but incomplete, skipped, or risky tests!
+Tests: 19, Assertions: 28, Skipped: 2.
+```
+