vim-language tool add `ignore` terms

Some hints about how to use it ? Maybe a tutorial ? I haven’t found anything about user-dictionaries, yet…

Actually, I have a concern about this. If I get it right, this file has to be suffixed with .dic, right ? But that is not OK for vim. vim requires the no-check file ends with .add

The ideal solution for me is:
LT accept an external ignore.(whatever). And I can point it directly to the ~/.vim/spell/en.utf-8.add

I’m looking at this part, according to @dnaber, shall I add a loop for the external ignore.txt ?