Add Zawadzki et al. to citation

[iancze]

We should also add Zawadzki+23 PASP to the citation info. If/when the JOSS paper is submitted and accepted, both should be suggested as relevant citations.

[jeffjennings]

Great.

"If/when"- I think there's no reason not to submit a JOSS paper. Its citation could replace the Zenodo citation.

[iancze]

I meant more about the acceptance, didn't want to be presumptuous ;)

[jeffjennings]

Ah ok gotcha. Updating things with the accepted JOSS paper is referenced in #203, so #228 should close this.