New App onboarding TODOS

[hdoupe]

• Use csk build-env by default to build app environments. (added by Backend docker image clean up / streamlining #396)
• Document social image link (Add social meta tags for data-visualizations #389)
• Document how to add images to app README
• Document how to add outside links to data viz (open in new tab) (Deploy app and data viz social media updates #393)
• Document / improve UI for setting location of viz app location and function name