Add example scripts to package.json

[Decipher]

Is your feature request related to a problem? Please describe.
As a contributor I want a script I can run from the root of the project so that I can run a druxt example.

Describe the solution you'd like

• Add a example:[folder] for each folder in the examples directory.
• Add example in the Gitpod welcome message.
• Add details in Contributor docs.

Describe alternatives you've considered
N/A

Additional context

• https://github.com/druxt/druxt.js/blob/develop/.gitpod/WELCOME.md
• https://github.com/druxt/druxt.js/tree/develop/examples