how can we maintain docs update

[arademaker]

delph-in/pydelphin#341 (comment)

The issue was about one thing; it ended up talking about something I didn't know about (UDF and UDX) and created the opportunity to update the wiki page. I didn't have time to update the page entirely, so I made a note about the pending issue in the end.

I know that this is not about ERG but relevant to ERG docs too. See @EricZinda (BTW, @emilymbender, another case you are collecting in https://github.com/delph-in/docs/wiki/ErgSemantics_Raw_Materials?)