Create/link to sample app

[drhuffman12]

Create/Update an example Crystal app that uses this shard; possibly w/ a'matrix' of version combo's made up of the:

• latest 2 versions of Crystal (stable? and nightly?)
• latest 2 versions of CouchDB (2.x? and 3.x?)

... either as part of this repo (probably not) or in a separate repo (with applicable links between in the docs).