feat: add contributing docs

CONTRIBUTING.md

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+# Contributing
+
+Contributions are welcome through GitHub pull request. This document outlines the steps to facilitate the acceptance of your contribution.
+
+## How to Contribute
+
+1. Fork repository, develop, and test your changes.
+2. Bump the chart version and update chart documentation.
+3. Submit a pull request.
+
+In order to make testing and merging of PR easier, please submit modifications to one chart in a separate pull request.
+
+### Technical Requirements
+
+* Must follow [charts best practices](https://helm.sh/docs/topics/chart_best_practices/).
+* Must pass CI jobs for linting and installing changed charts with the [chart-testing](https://github.com/helm/chart-testing) tool.
+* Any change to a chart requires a version bump following [semver](https://semver.org/) principles. See [Immutability](#immutability) and [Versioning](#versioning) below.
+
+Once changes have been merged, the release job will automatically run to package and release changed charts.
+
+### Immutability
+
+Chart releases must be immutable. Any change to a chart, including documentation updates, requires bumping the chart version.
+
+### Versioning
+
+The PATCH version in the `Chart.yaml` should be bumped for any changes to the chart.
+
+### Generate documentation
+
+The documentation of each chart can be re-generated with the following command:
+
+```shell
+make docs
+```
+
+### Community Requirements
+
+This project is released with a [Contributor Covenant](https://www.contributor-covenant.org).
+By participating in this project you agree to abide by its terms.
+See [CODE_OF_CONDUCT.md](./CODE_OF_CONDUCT.md).