Library has inadequate documentation in the docs directory

[thomashoneyman]

Is your change request related to a problem? Please describe.
As described in the documentation section of the Library Guidelines, Contributors libraries are expected to have some documentation in the docs directory -- specifically, a changelog and at least a short tutorial that expands on the quick start in the README.

This library currently doesn't have any extra documentation in the docs directory.

Describe the solution you'd like
The argonaut-codecs docs directory has a good example of expanded documentation for a Contributor library. But it would even be useful to add something considerably smaller and shorter to this library.

We could add an expanded version of the quick start -- breaking down the most important types and functions in the library and then explaining how to create and use common formatters for things like numbers, dates, RFC3339 strings, and so on.

Additional context
See the Governance repository for more information about requirements in the Contributors organization.