Add a "How to cite" section to README?

[jchodera]

Now that there is data that can be downloaded and used, it would be helpful to add a section to the README.md on "How to cite the Spice dataset" with information on how to cite this dataset so that the folks who have put in a lot of effort (@pavankum @peastman @dotsdl) can get credit for their work.

This could be something similar to what MDTraj uses.

We could also activate the Zenodo github integration and have Zenodo mint a DOI acknowledging the contributors when a new GitHub release is cut, and then we can add the badge to this repo's README.md.

[peastman]

I guess that citing this repository is the best we have right now. We should aim to get a paper submitted as soon as possible after the dataset is complete. That's still a few months away, but I can start writing it up.

[jchodera]

@peastman : Can you add both the arXiv citation and the Zenodo DOI (and badge) to the README?