Task: Make this repository citeable

[matt-graham]

What needs to be done?

We should add a CITATION.cff file to make it clear how to cite this repository itself, particularly as we're starting to think about advertising more widely. Relatedly we may also want to set up the Zenodo integration for the repository if we haven't already done so we get DOIs when we make a release.

### Tasks
- [x] Enable Zenodo integration
- [x] Add `CITATION.cff` file

[paddyroddy]

I had wondered about this recently 🤔 prompted by the Code for Thought podcast recently

[matt-graham]

Now that GitHub allows linking ORCIDs to profiles it feels like there should be a way to automate keeping the author list on a CITATION.cff up to date (assuming this is based on contributor list, potentially with some filtering) 🤔

[paddyroddy]

I'm still a bit confused what the ORCiD bit is doing in CITATION.cff. Like it doesn't appear in the output Roddy, P. J. (2023). SLEPLET: Slepian Scale-Discretised Wavelets in Python. Journal of Open Source Software, 8(84), 5221. https://doi.org/10.21105/joss.05221

[matt-graham]

The Zenodo integration automatically picks up ORCIDs from the CITATION.cff file I think for example (e.g. https://zenodo.org/records/10144016). I think the purpose of the file is more general than the GitHub usage.

[paddyroddy]

Maybe you're right. I know mine has picked up the ORCiD here doi.org/10.5281/zenodo.7268074, but that could have easily been from my Zenodo account (like I wouldn't need CITATION.cff to achieve the same). But maybe for co-authors it is necessary...

[paddyroddy]

Related zenodo/zenodo#596

[samcunliffe]

I guess we want a DOI for the pages too?