Missing contributing.md?

[astrochun]

It's unclear whether DRAGONS is accepting contributions. Assuming that the DRAGONs team wishes to receive them, having a CONTRIBUTING.md will encourage other OSS developers in the astronomy field to contribute.

Here are just a few public examples of good CONTRIBUTING.md and with "How-To" instructions:

1. https://gist.github.com/PurpleBooth/b24679402957c63ec426
2. Auth0's: https://github.com/auth0/open-source-template/blob/master/GENERAL-CONTRIBUTING.md
3. https://github.com/nayafia/contributing-template/blob/master/CONTRIBUTING-template.md