Adding documentation that is provided in Readme to hex

[the-shank]

Thanks for this very useful library!

As it currently stands, all the usage related documentation is provided in the README file and none of that is reflected in hexdocs. It would be useful to add this documentation or at-least some part of it to the docs for the library.

Please let me know if this sounds like a good idea. I shall send a PR accordingly.

[isaacsanders]

I think this is a good idea. Documenting it to match the sort of documentation found for the :console logger backend could make it easier to discover the documentation.