Include CI and test coverage

[crhea93]

As per the review template for the PyOpenSci submission, please include CI and test coverage badges. It is also useful to have codecov, but this is not a requirement.

This issue is part of the PyOpenSci review at pyOpenSci/software-submission#250

[SimonMolinsky]

Hi @crhea93

I've added both badges to the README, code coverage is estimated using Github Actions.