See cross-doc references at source doc

I’m doing some Coda clean-up and wanted to delete a few tables. Problem is, I’m not sure if they’re being used through a cross-doc connection elsewhere.

That puts me in a bind - I might delete it and irreparably break a different document and not know it. Just like I can see that a table is being used by other tables, it’d be great if there was information on its cross-doc usage.