Community Guidelines: How does a user contribute?

[hayesall]

Recommendation: Add CONTRIBUTING.md with brief notes for how to contribute:

1. What contributions would be helpful (bug reports, patches, documentation)
2. Is there a formal review process, etc.

GitHub suggests placing these in a CONTRIBUTING.md file, which GitHub looks for in a .github/ directory at the base of a repository.

[elwinter]

README.md was updated with instructions for providing bug reports and code contributions.