Improve app review process

[bkeepers]

Our process for adding new apps to the site is very minimal right now. Here are a few things I'd like to see improved:

• Clearly define requirements for apps that will be added to the site (unique functionality, commitment to uptime, etc) in docs
• Ask users to turn on GitHub Pages builds for their fork, and include a link to their app (e.g. https://bkeepers.github.io.org/probot.github.io/apps/stale/) - this will first require some fixes to the site to allow it to render properly on forks.
• Use PR template with checkboxes to talk people through the process of submitting an app

[stale]

Is this still relevant? If so, please comment with any updates or addition details.

[hiimbex]

I still think this would be an ideal world for the website 👍