Add use cases vignette/table

[seabbs]

This package is used both by many of our downstream projects and by other research projects. As is fairly usual citing has been quite poor but a quick scan of GitHub flags quite a few public projects that have made use of the package.

It might be helpful to flag some of these in a vignette. This could take the form of an interactive table or similar.

To get this started I can put something together using my projects that use the package but it would be nice to widen this.

[seabbs]

Tagging a few people who may have made use of the package (please feel free to either ignore or if interested post a link to anything using covidregionaldata with a short blurb): @yangclaraliu, @nicholasdavies, @thimotei, @amygimma, @pearsonca

Apologies if tagged in error.

[seabbs]

In dev draft lists some use cases: #323

[github-actions]

This issue has been flagged as stale due to lack of activity