Clarify Codecov requirements

[bschilder]

I believe Codecov has changed how their service integrates with GitHub a couple times, and I'm not totally clear on whether any of these are true:

1. Codecov requires a CODECOV_TOKEN GH secret in each repo.
2. Codecov requires a CODECOV_TOKEN GH secret at the organisation level.
3. Codecov does not require any token, but does require users change the Settings of their repo/org to enable Codecov.
4. Codecov does not require any setup whatsoever beyond running the rworkflows covr steps and uploading the results.

Once I figure this out, I'll add some instructions for the user in both the README, use_worklow, and action.yml documentation.

[bschilder]

1. Codecov requires a CODECOV_TOKEN GH secret in each repo.

False

2. Codecov requires a CODECOV_TOKEN GH secret at the organisation level.

False

3. Codecov does not require any token, but does require users change the Settings of their repo/org to enable Codecov.

The official Codecov docs say this is True:

If you are a Github user you MUST install the Codecov GitHub app for your organization - Codecov can't function without it.

....but I'm seeing the exact opposite in practice. For example, in the neurogenomics Org app settings, I see Codecov is not installed:

Nor is it installed at the level of the rworkflows repo:

Nor do i have any secret variables (at the Org or repo levels) that would enable codecov that way:

So perhaps their docs are wrong or outdated?

Or perhaps something about how the rworkflows action (or its subactions) is setup already circumvents this?

4. Codecov does not require any setup whatsoever beyond running the rworkflows covr steps and uploading the results.

It would appear this is the case, despite the Codecov documentaton.