Document GitHub Workflows and testing process for quickstart contributions

[kendallroden]

Describe the feature

In order to contribute new tutorials or quickstarts there is a validation process in place using GitHub actions. There is no contributor guide that explains the requirements for quickstart tests or what the tests validate. It would be good to have documentation in the quickstart repo around this process so that people can better contribute tutorials/quickstarts

[paulyuk]

We've had WIP here and it's almost done.
#977