Expand explainer

[slightlyoff]

This explainer is good!

I'd like to see a few things expanded on:

• enumerate non-goals
• provide an "open design issues" section
• flesh out the list of prior work to include some of the more popular Node/Electron modules (e.g. node-desktop-idle, the Electron powerMonitor module, etc.)
• add a "Considered Alternatives" section to discuss tradeoffs and different available API style options
• expand example code to show how the provided sample code addresses the provided list of use-cases
• in example code, show how this API will integrate with (and be used around) the Permissions API
• discuss how this API integrates with existing APIs that provide some info in this area (Page Lifecycle API, Page Visibility API, etc.)
• outline or discuss integration into worker contexts, specifically Service Workers