Explicitly state, or document, which "source book abbreviation"s are supported for imports.

[Charlweed]

I want to add some monsters to my map. I go to 00.DM and select the "Lib:DDB Importer" token. But if I click the "Import" button in the Selected window, I do not know what I can put into the "Source:" field. actually, I think I can use the string "DDBI" but that is just a guess from following the wiki, which is out of date. BTW: I just dropped some cash in the Patreon jar, because this project clearly deserves it.