Example of adding a function and some added repo materials

[boshek]

Contained herein:

• Adding some general guidelines for contributing. These are taken mostly from ropensci. These documents can certainly be modified to suit our needs but the location makes sense as the .github folder ensures they provide info when opening issues and submitting pull requests.
• Adding a code of conduct while also can easily be modified. Helpful for contributing.
• Adding a NEWS.md file that can track changes to the package.
• Adding a water year function to illustrate how a function could be added (including a unit test)