Improve documentation

[radbrt]

This is in part thinking out loud, and thinking back on how I learned (and was confused by) Meltano. I want to take some time update the documentation now that we have moved to meltanolabs.

1. Since we moved the repo to meltanolabs, maybe we should change the example singer-based json config with a meltano-based yaml config. It might take a little effort for new users to mentally "convert" the json config into yaml.
2. This might be a pet-peeve of mine, but I would like to document some of the options and edge-cases regarding possible unique keys, and give some usage examples. This might be too long for the README though, so maybe we want to do this in a different place. Maybe the wiki, or a separate docs folder?
3. Development/tox tests might be a bit esoteric, maybe move this to a separate readme inside the tests folder?
4. Add links to general meltano docs? I keep wanting do document things that are really general Meltano features, so this is perhaps a way to avoid that.

[pnadolny13]

@radbrt I think this is a fantastic idea! I think getting some meltano references in here would be a great starting place. Ideally we'd convert this to an SDK based tap which usually isnt all that hard since the code is all written and it just needs to be migrated to the SDK structure.