Create CONTRIBUTING.md

Signed-off-by: Marijn van Wezel <96489967+marijnvanwezel@users.noreply.github.com>

.github/CONTRIBUTING.md

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+# Contributing to php-cypher-dsl
+
+Welcome! We look forward to your contributions. This document outlines the guidelines for contributing to php-cypher-dsl. Keep in mind that these are just suggestions, and shouldn't hold you back from making improvements to php-cypher-dsl. Don't be afraid to ignore the rules.
+
+Below are some examples on how you can contribute:
+
+* [Report a bug](https://github.com/neo4j-php/php-cypher-dsl/issues/new?template=bug_report.md)
+* [Propose a new feature](https://github.com/neo4j-php/php-cypher-dsl/issues/new?template=missing_feature_request.md)
+* [Send a pull request](https://github.com/neo4j-php/php-cypher-dsl/pulls)
+
+## Code of conduct
+
+This project has a [Contributor Code of Conduct](https://github.com/neo4j-php/php-cypher-dsl/blob/main/CODE_OF_CONDUCT.md). By contributing to or participating in this project, you agree to abide to its terms.
+
+## Any contributions will be licensed under the GPL 2.0 or any later version
+
+When submitting code or changes, your submissions will automatically be licensed under the [GNU General Public License](https://github.com/neo4j-php/php-cypher-dsl/blob/main/LICENSE) version 2.0 or later. By contributing to this project, you agree that your contributions will be licensed under its terms.
+
+## Writing bug reports
+
+In your bug report, you should provide the following:
+
+* A short summary of the bug
+* What you expected would happen
+* What actually happens
+* Steps to reproduce
+** Be specific!
+** Give sample code if possible.
+** Include the version of PHP and php-cypher-dsl.
+
+You should only report bugs for versions of php-cypher-dsl that [are supported](https://github.com/neo4j-php/php-cypher-dsl/blob/main/LIFECYCLE.md). Please only report bugs if you are using a php-cypher-dsl with a [compatible version of PHP](https://github.com/neo4j-php/php-cypher-dsl/blob/main/LIFECYCLE.md).
+