Add CONTRIBUTING.md (#83)

Author: ocean90

CONTRIBUTING.md

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+# Contributing
+
+The required coding standards represent the best practices for enabling a consistent code style across the team. As the way we work evolves over time, our coding standards likewise need to evolve.
+
+## Rule Changes
+
+For changing or adding rules please start a new issue and/or submit a pull request for discussion.
+
+## Releasing
+
+All notable changes to this project must be documented in the [CHANGELOG.md](CHANGELOG.md) file. The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/) and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+The project consists of one PHP package (published on [packagist.org](https://packagist.org/users/wearerequired/)) and two JavaScript packages (published on [npmjs.com](https://www.npmjs.com/org/wearerequired)). All packages must be published with the same version.  
+For dependent package management this project uses [Lerna](https://lerna.js.org/).
+
+### Releasing Packages
+
+If you haven't yet, run `npm install`.
+
+Lerna automatically releases all outdated packages. To check which packages are outdated and will be released, type `npm run publish:check`.
+
+If you have the ability to publish packages, you must have [2FA enabled](https://docs.npmjs.com/about-two-factor-authentication). Confirm that you're logged in to npm, by running `npm whoami`. If you're not logged in, run `npm adduser` to login.
+
+#### Development Release
+
+Run the following command to release a dev version of the outdated packages.
+
+```shell
+npm run publish:dev
+```
+
+Lerna will ask you which version number you want to choose for all packages. For a `dev` release, you'll more likely want to choose the "prerelease" option.
+
+Lerna will then publish to npm, commit the `package.json` changes and create the git tags.
+
+**Note**: If Lerna doesn't detect any changes since only the PHP package was updated use `--force-publish`.
+
+```shell
+npm run publish:dev -- --force-publish
+```
+
+#### Production Release
+
+To release a production version for the outdated packages, run the following command:
+
+```shell
+npm run publish:prod
+```
+
+Choose the correct version based on the [CHANGELOG.md](CHANGELOG.md) file, confirm your choices and let Lerna do its magic.