If you didn't happen to notice this is a live editor (you can make any changes you'd like), with live documentation. You can paste an existing file to get help information, or write a new one live in the editor.
This is going to be very useful. Finding substantive documentation for package.json has always been a bit of a struggle (there's a page on npmjs.org, but it takes longer to find than it should).
Great reference! Would be nifty if documentation on properties (e.g. `scripts` in `package.json`) were linkable for sharing and bookmarking.