Default destination in `cff_write_citation` is in a temporary folder

[roaldarbol]

Hi there, thanks for this package!

I was walking through #51 to generate a inst/CITATION file, and it's mention in https://github.com/ropensci/cffr/issues/51#issuecomment-1523322283 that the default location is inst/CITATION, but it seems the default actually is a temporary folder. Is that a bug or a feature? I think the mentioned default makes a lot of sense, as that's exactly where you'd expect it to end up. :-)

> cff_write_citation(cff_obj)
ℹ Writing 2 entries ...
✔ Results written to /var/folders/rh/y9ws4bgj7x50twypcwtk2ypr0000gp/T//Rtmp8cLQvY/CITATION_6d794bd1d97