Add a contributors file

[matthewfeickert]

pandamonium is made better by the people who were kind enough to hack on it and make a drive-by PR. Giving them a nod by adding their name to a contributors.md file would be nice.

This is motivated by how pyhf does things but you can get even fancier like awkward does with a bot.

[dguest]

isn't that what the zenodo file does?

[matthewfeickert]

No, the Zenodo config file is meant to be for the authors / copyright holders.

https://github.com/dguest/pandamonium/blob/5650c0de68f74644489984ae576041f319e4686b/.zenodo.json#L7-L18

but if you don't tell Zenodo anything then it thinks that everyone who has contributed is an author / owner.