User-friendlier interface for email storing (Polite Pool)?

[maelle]

At the moment the email address is stored in .Renviron which is not easy (although one can get used to it, and use usethis::edit_r_environ()).

Could rcrossref use some app dir instead? There'd be a function rcrossref::register_email() where one could provide the email address as argument / type it in the console and it'd be stored somewhere in a directory found with tools::R_user_dir().

There could also be a function rcrossref::remove_email() or so.