Outline for Automated Cron module guide

For context see #2887480: Outline, standardize, and complete documentation for Drupal 8 core modules.

Proposed outline

Here's a proposed outline for what the documentation for the guide at https://www.drupal.org/docs/8/core/modules/automated_cron should contain.

• Page: Automated Cron module overview
  What is cron?

  Module description, and example use cases. What does this module do? When should I enable it?

  Start by copy pasting from help text displayed by the help module at admin/help/automated_cron, and adjust

• Page: First steps
  Documents typical next steps when using the module, configuration, terminology, and concepts.
  • Notes about what this should cover
  • What is cron?
  • Allows cron to run automatically when pages are visited.
  • Pros and cons to using this menthod vs setting up cron.
• Related: Setting up cron

Next steps

• Review above outline and suggest changes
• Review and update existing overview page
• Draft pages in guide and publish for review