Contribution guide for Quickstart

[msfussell]

This issue is to provide guidance on contributions to the Quickstart repo, including

• Mechanical Markdown guidance
• How to create a sample based on an issue.

[msfussell]

@marcduiker for viz

[paulyuk]

I agree with this idea. Starting now as I go through the process for 1.13 :)

[marcduiker]

I agree with this idea. Starting now as I go through the process for 1.13 :)

Great! Once the written version is there, I'll create a video about contributing to the Quickstarts repo.