Print a warning when running `skunk` without a `coverage/.resultset.json`

[etagwerker]

In the README.md:

To get the best results, make sure that you have coverage/.resultset.json in
your application directory. That way skunk knows what's the status of your
test suite + code coverage.

Running skunk without that file is kind of pointless. The whole idea of the "StinkScore" is to combine RubyCritic's cost with SimpleCov's lack of coverage, in order to get a realistic "StinkScore"

So we should make sure the user understands that the scores that they're getting is not that useful.

[bronzdoc]

If the result without coverage/.resultset.json is not useful then we should make it a requirement to run skunk

[bronzdoc]

ping @etagwerker

[etagwerker]

@bronzdoc I don't think we should make it a requirement, I think it should output a noticeable warning. We have to assume that sometimes a project has no test suite, so they won't have code coverage data, but as they add coverage to their codebase, they might want to see the evolution of their stink score average (related to #5)

[FionaDL]

@etagwerker @bronzdoc Maybe there should also be a note in the documentation about having to change the path within the file?

[etagwerker]

@FionaDL I think that is an issue in SimpleCov, not skunk -> https://github.com/colszowka/simplecov

I think it would be useful if SimpleCov had a way to generate coverage/.resultset.json with relative paths, instead of absolute paths.