Improve non-code contributing guidelines

[oleg-nenashev]

Currently the non-code contributions are rather a second class citizen in the documentation. It would be great to provide better contributing guidelines to those who want to contribute to other areas, e.g. documentation or artwork.

Scope

• https://keptn.sh/community/contributing/ is updated to include non-code contributions. Contributor Guide: Document non-code contributions keptn.github.io#989
• Documentation contributor guidelines are updated for the key repositories -
• There is a default issue template for documentation available in the repositories
• There is a repository for artwork contributions - Create an artwork repository for Keptn artwork #65

[agardnerIT]

@StackScribe @staceypotter is this still relevant (with your current work) or can we close?

[oleg-nenashev]

I believe most of the issues on the list were addressed. From what I recall there still no decent contributing guidelines for Keptn extensions, not sure about the KLC