contributing notes

Author: alecrabbit

CONTRIBUTING.md

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+# How to Contribute
+
+## Before creating a Pull Request
+
+* Create an issue to discuss a necessity of such pull request 
+
+## Pull Requests
+
+* Fork the `<PACKAGE_OWNER>/<PACKAGE_NAME>` repository
+* Create a new branch for each feature or improvement
+* Send a pull request from each feature branch to the **master** branch
+
+It is very **important** to separate new features or improvements into separate feature branches, and to send a
+pull request for each branch. This allows us to review and pull in new features or improvements individually.
+
+## Style Guide
+
+All pull requests must adhere to the [PSR-12 standard](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-12-extended-coding-style-guide.md).