Add rworkflows GitHub Actions

[bschilder]

Hi @rcorces , now that it's reached maturity I thought you might be interested in using rworkflows for running continuous integration directly in GitHub Actions.

You can read more about all the things it can automate here: https://github.com/neurogenomics/rworkflows

Let me know if you have any questions about it, or any feature requests and I'd be happy to accomodate!