Improve README and add subsequent documentation on current checks

[seanmarpo]

Description

The README leaves a lot to be desired in terms of ease-of-use. Most notably, pipenv usage is inherently confusing to folks that haven't used it before.

Also, it would be nice to have docs specific to how the parts of CSRT work together for others that have an interest in improving the project.

Lastly, we need a doc that outlines the checks we currently perform and our relevant level of confidence in the check. This will provide the transparency needed for folks that want to incorporate this tooling into a build/test pipeline.