Add reference field for affiliated registry

[bsipocz]

It would be great to have a field for the preferred reference for the affiliated packages so it's easier for users to figure out what to cite.

[pllim]

@lwasser , does pyOpenSci listing come with citation stuff?

[lwasser]

@pllim @bsipocz we capture both the joss doi and a zenodo doi if users provide that . it's not on the website yet but I have a plan to add it. Is that what you mean? Doi links in our yaml file?

[pllim]

Doi links in our yaml file?

I think so... but I will let Brigitta confirm.

[bsipocz]

yes, doi links to papers and/or zenodo releases. Please note that for many packages are published as ApJ or similar rather than JOSS, so the field should require some flexibility.