How do you create a manifest file to be used with a local package in the package manager?

I see that you can add a local package to the Package Manager in 2018.3 which requires a package.json. This file's contents require a name which follows the standard android application format of "com.company.product". I'm unsure of how to create a manifest file that can link to a specific package (I've exported a .unityPackage with a sample script in it to test this) that can be read by the Package Manager. Does anyone have any materials on how to do this?