new feature: add repo citation file

[scrasmussen]

TYPE: new feature

KEYWORDS: citation, cff file

SOURCE: Soren Rasmussen, NCAR

DESCRIPTION OF CHANGES: Initial version of a CITATION.cff file, a Github repo citation file. Note that the first Zenodo identifier listed in the file is the one for all versions of WRF-Hydro and specific versions are listed below it. This helps solve the chicken-and-egg problem of creating a new Zenodo release but documentation pointing to the old version.

The authorship order is based on number of git commits, this can be manually changed in the file and we should discuss that order before merging. I believe that once the CITATION.cff file is added Zenodo will take it's authorship order from it for future releases. Here is an example screenshot of what the repo homepage will look like:

TESTS CONDUCTED: text only change.

Checklist

• [ ] Closes issue #xxxx (An issue must exist or be created to be closed. The issue describes and documents the problem and general solution, the PR describes the technical details of the solution.)
• [ ] Tests added (unit tests and/or regression/integration tests)
• [X] Backwards compatible
• [ ] Requires new files? If so, how to generate them.
• [ ] Documentation included
• [ ] Short description in the Development section of NEWS.md

[scrasmussen]

@rcabell good idea about the ORCIDs! I'll try to track some down.

I put it as draft because I wanted to discuss the author order in a PR meeting before merging. Given the long history of the code maybe there are authors that should be listed that aren't, maybe a different order would be more appropriate?