codemeta json for compendia

[benmarwick]

I heard recently that rOpenSci will soon be asking for codemeta.json metadata for submissions to their family of packages. They may be able to simplify this with a new function usethis::use_codemeta() which would use https://github.com/ropensci/codemetar. This metadata format is widely accepted by many trustworthy repositories.

We might want to consider this too. Perhaps we could auto-generate this json file during rrtools::use_analysis() or some other point after the DESCRIPTION is well-populated? And then prompt the user to update it later maybe?

[benmarwick]

Add an informational last step in our readme about how to deposit the compendium on a repository