added contributing & code of conduct

Signed-off-by: André Bauer <[email protected]>

CODE_OF_CONDUCT.md

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+# Community Code of Conduct
+
+Kokuwa.io follows the [CNCF Code of Conduct](https://github.com/cncf/foundation/blob/master/code-of-conduct.md).

CONTRIBUTING.md

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+# Contributing Guidelines
+
+Contributions are welcome via GitHub pull requests. This document outlines the process to help get your contribution accepted.
+
+## Sign off Your Work
+
+The Developer Certificate of Origin (DCO) is a lightweight way for contributors to certify that they wrote or otherwise have the right to submit the code they are contributing to the project. Here is the full text of the [DCO](http://developercertificate.org/). Contributors must sign-off that they adhere to these requirements by adding a `Signed-off-by` line to commit messages.
+
+```text
+This is my commit message
+
+Signed-off-by: Random J Developer <[email protected]>
+```
+
+See `git help commit`:
+
+```text
+-s, --signoff
+ Add Signed-off-by line by the committer at the end of the commit log
+ message. The meaning of a signoff depends on the project, but it typically
+ certifies that committer has the rights to submit this work under the same
+ license and agrees to a Developer Certificate of Origin (see
+ http://developercertificate.org/ for more information).
+```
+
+## How to Contribute
+
+1. Fork this repository, develop, and test your changes
+1. Remember to sign off your commits as described above
+1. Submit a pull request
+
+***NOTE***: In order to make testing and merging of PRs easier, please submit changes to multiple charts in separate PRs.
+
+### Technical Requirements
+
+* Must pass [DCO check](#sign-off-your-work)
+* 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 warrants a chart version bump even if it is only changed to the documentation.
+
+### Versioning
+
+The chart `version` should follow [semver](https://semver.org/).
+
+Charts should start at `1.0.0`. Any breaking (backwards incompatible) changes to a chart should:
+
+1. Bump the MAJOR version
+2. In the README, under a section called "Upgrading", describe the manual steps necessary to upgrade to the new (specified) MAJOR version
+
+### 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).